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477Ambio Vol. 29 No. 8, Dec. 2000 © Royal Swedish Academy of Sciences 2000http://www.ambio.kva.se

INTRODUCTIONRainwater harvesting implies collection and storage of the rainyseason precipitation that would have seeped into soil or run offinto stream channels. It is an old technique that was probablydeveloped as long ago as 4500 B.C. (1, 2). Although earlier rain-water harvesting systems were designed primarily to meet do-mestic needs for water, in recent decades, scientists in manycountries such as Sub-Saharan Africa, the Middle East andSoutheast Asia, and especially India, have made efforts to de-sign and develop a wide variety of techniques to collect, store,and use natural precipitation for agricultural purposes (3–13). Insome countries, development of rainwater harvesting systems isbeing promoted by the authorities as an alternative to the high-cost large dams and water development projects (14). China hasa long history of rainwater harvesting techniques in many wa-ter-deficient areas such as the Loess Plateau. This dates back tothe Qing and Han Dynasties about 2000 years ago (15). Whileenabling people to survive in drought-prone environments, thewater yield from early rainwater harvesting techniques is not suf-ficient for modern agricultural purposes (15). Since the mid-1980s, scientists in Gansu province have worked to design mod-ern forms of rainwater harvesting, which will be suitable for ag-ricultural irrigation. An effectively designed system for watermanagement on rainfed cultivated land was first developed overa decade ago. This system is termed rainwater harvesting agri-culture (RHA). During the last 10 years, RHA has been success-

Article Fengrui Li, Seth Cook, Gordon T. Geballe and William R. Burch Jr

Rainwater Harvesting Agriculture:An Integrated System for Water Management onRainfed Land in China’s Semiarid Areas

fully applied by many household farmers in semiarid areas ofGansu and other provinces in northwest China. The purpose ofthis paper is to give a general picture of the principles and meth-ods of RHA as well as its recent development in China’s semi-arid areas, especially in Gansu province.

WATER CONSTRAINTS TO RAINFED FARMING INCHINA’S SEMIARID AREASChina’s semiarid areas extend across almost the whole country(Fig.1). It includes much of northwestern China, particularlyGansu, Qinghai, Ningxia, Shanxi, Shannxi and Inner Mongoliaprovinces with a total area of 1.7 mill. km2, about 18% of thenation’s territory. Annual rainfall throughout the region rangesfrom 250 to 600 mm. Annual accumulated temperature, ≥10°ranges from 1500 to 4500°C. Annual frost-free period variesfrom 120 and 190 days. The major soil categories in the culti-vated land area are loamy sand, loess sandy loam and blacksandy loam. These soils are loosely structured and coarse tex-tured and thereby are highly susceptible to erosion by water andwind (16). Three principal land-use management systems domi-nate this region. In some drier parts of the region where aver-age annual rainfall is below 300 mm and no water resources areavailable for agricultural irrigation, rangeland pastoralism iscommonly practiced. In other drier parts of the region where,although average annual rainfall is less than 300 mm, surfaceand/or ground-water resources are available, irrigated agricul-ture is usually carried out. In a large area of the region receiv-ing a mean annual rainfall of over 300 mm, rainfed farming isthe most widespread land-use practice. Overall, rainfed croplandoccupies nearly 80% of the total cultivated land in the region(17).

Although the level of agricultural productivity in the prevail-ing rainfed farming system is restrained by many biophysical fac-tors, the most serious limit is low availability of water. This re-

Rainwater harvesting agriculture (RHA), which was firstdeveloped by scientists in Gansu province over a decadeago, is an integrated system for water management onrainfed land in semiarid areas. This system consists ofthree main components including rainwater harvestingsystem, water-saving irrigation system, and highly effectivecrop production system. Its main function is to providefarmers in water-limiting environments with access to thewater needed to meet domestic and agricultural waterneeds. The preliminary implementation of RHA in Gansuand other provinces in northwest China suggests that RHAhas the potential to improve performance in rainfed farmingsystems and to address environmental problems such assoil erosion. The small-scale and low cost of RHA systemsmake application by household farmers simple. However,to be successful RHA needs to be integrated in a com-prehensive agricultural-management system; i.e. manage-ment of RHA must be combined with other agriculturaltechnologies and management practices. In addition, thespread of RHA over large areas entails consideration of arange of technological, agrohydrological, ecological, social,cultural, economic, and political factors. In particular, thereis a need to provide training and extension services tofarmers, to develop and disseminate more effective andaffordable types of RHA technologies as alternatives andto design and develop alternative policy instruments andsocial institutions that facilitate adoption of RHA practices.

Figure 1. Map of rainfall distribution in China.

Gansu province

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478 © Royal Swedish Academy of Sciences 2000 Ambio Vol. 29 No. 8, Dec. 2000http://www.ambio.kva.se

gion is strongly governed by the prevailing monsoon climate,whereas the monsoon rains are highly variable in terms of theiramount and reliability. Hence, not only is the total amount ofrainfall often inadequate, but also it is subject to the high inter-annual and interseasonal variations (18, 19). On average, ap-proximately 60% of the annual rainfall usually falls during thethree months between July and September, often in the form ofheavy thunderstorms. This causes not only tremendous amountsof erosion, but also problems of frequent and serious spring andearly-summer drought for both winter and summer crops. Somestudies in a semiarid region of Gansu province show that themain water stress period for winter crops, such as winter wheat,often occurs from May until the start of the rainy season in July,whereas the main water-stress period for summer crops such ascorn often occurs during the period from mid-June to early-Au-gust (Table 1). As the periods of water stress for both winterand summer crops coincide with their heading and grain-fillinggrowth stages, it is extremely unfavorable for grain production(20). For this reason, providing supplemental irrigation to cropsduring their water-stress periods is essential to achieve a high,sustainable yield in rainfed conditions.

For a long period of time, particularly since the founding ofthe People’s Republic of China in 1949, the main strategy foragricultural resource management on rainfed land in China’ssemiarid areas has been known as water-soil conserving farm-ing (WSCF) (21, 22). A significant feature of WSCF is the con-struction of terraced fields on hillsides to retain runoff and pre-vent soil erosion. The principal technological components of thissystem include intensive cultivation (e.g., ploughing, raking andlevelling of cropland), integrated application of inorganic andorganic (e.g., farm and green manure) nutrients, stubble, gravel

and plastic film mulches, cropping system practices (e.g., croprotation, ley farming, intercropping and multiple cropping) andthe choice of improved crop varieties. Many studies indicate thatadoption of WSCF practices has led to a significant increase incrop productivity on rainfed land as a direct result of improvedavailability of water and nutrients for crops. For instance, theaverage yields of wheat crops on terraced fields have increasedfrom 1500–1800 kg ha–1 in the 1950s to 2200–2500 kg ha–1 inthe late-1980s, in areas with annual rainfalls of about 450 mm(22). At the same time, WSCF has also played a beneficial rolein conserving soil and water resources. In spite of being invalu-able for alleviating erosion and increasing productivity, conven-tional WSCF can not solve the fundamental problem of poorwater availability (23). At present crop production levels, the wa-ter availability for crops is below minimum requirements for fullyields in the semiarid areas. Thus, inadequate water supplies area major constraint for sustainable crop production. An increasein crop yield will depend on whether water availability can beincreased.

According to our study in a semiarid region of Gansu prov-ince (19), the relative water satisfaction of winter wheat, definedas the percentage of growing-season precipitation relative to cropwater requirements for full yield is 62% in terms of the wholephenology and only 35, 41, and 40% for the 3 critical growthstages of jointing, heading and grain-filling. The relative watersatisfaction of corn is 87% for the whole phenology, but only55 and 79% for the 2 critical growth stages of jointing and ear-ring (Table 2). Some other studies in the same region also indi-cate that the relative water satisfaction of grain crops ranges from60 to 90% in areas with annual rainfall between 450 and 600mm and only from 40 to 60% in areas with annual rainfall be-tween 300 and 450 mm (24). Such a large water deficit is im-possible to compensate for simply by implementing conventionalWSCF practices (23).


Rainwater Harvesting Agriculture and Its TechnologicalSystemsIt is evident that rapid, effective and low-cost solutions to theproblems relating to inadequate water availability are necessaryto increase yields and sustainable development of rainfed farm-ing in China’s semiarid areas.

The development of large-scale irrigation developmentprojects which depend largely on massive and permanent watersources such as stream water and river water, may offer a po-tential solution to the problem, but this is not always the casefor several reasons. (i) Both surface and groundwater resourcesare scarce in most of China’s semiarid areas. In some parts ofthe region although groundwater is available, it is often highly

Table 1. Relationship between the supply and demand of rainfallduring different growth stages of winter wheat and corn in asemiarid region of Xifeng (long-term mean annual rainfall561 mm) in Gansu province.

Rainfall Potential Water Relative(mm) ET deficit crop water

Phenology mean ± SD (mm) (mm) satisfaction (%)

Winter wheatSowing-regrowth 122±52 105 – 100Regrowth-elongation 34±19 98 –64 35Elongation-heading 48±31 116 –68 41Heading-grainfilling 42±29 103 –61 41Grainfilling-mature 41±32 36 – 100Whole phenology 286±75 458 –172 62

CornSowing-elongation 109±44 199 –90 55Elongation-earing 97±51 122 –25 79Earing-grainfilling 106±58 116 –10 91Grainfilling-mature 88±54 34 – 100Whole phenology 399±96 461 –62 87

% = as a percentage of the rainfall during different growth stages relative topotential evapotranspiration (i.e. crop water requirements for full yield).

Table 2. Onset, duration and end of the water stress periods for winter wheat and cornwith different soil layers in a representative dry and wet year in a semiarid region ofXifeng in Gansu province.

Dry year Wet year Duration (days)Layer(m) Onset End Onset End Dry year Wet year

Winter wheat0.0–0.5 17 May 13 July 8 May 26 June 58 500.5–1.0 24 May 16 July 24 May 6 June 54 141.0–2.0 8 June 14 July None None 37 None

Corn0.0–0.5 10 June 14 Aug. None None 66 None0.5–1.0 5 June 22 Aug. None None 18 None1.0–2.0 None None None None None None

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saline or brackish and thus cannot be used for either irrigationor human consumption. (ii) Almost 80% of the cultivated landin the region consists of highly fragmented hillside slopes re-sulting from the extensive mountainous and hilly topography.In the case of Gansu province, some 62% of the cultivated landis slopes with a steepness of between 3 and 15°, 23% consistsof slopes with between 15 and 25° and 6% has slopes steeperthan 25°. From an ecological perspective, less than 10% ofGansu’s cultivated land is suitable for agricultural activities. Thetopography makes large-scale irrigation projects difficult to de-velop. (iii) The soils in the region are loosely structured andhighly susceptible to wind and water erosion and thus the con-struction of large-scale irrigation works may cause environmentalproblems such as subsidence and soil erosion. (iv) The high costsof large-scale irrigation development projects are prohibitive inpoor areas with very limited financial resources. (v) High con-struction, operation and management costs are likely to trans-late into relatively high prices for the use of irrigation water,which farmers in poor areas are virtually unable to afford.

If large-scale irrigation development projects are not the an-swer to the problem of water shortages in semiarid mountain-ous and hilly areas in northwestern China, then what is? In or-der to be feasible, any workable solution must be affordable andcompatible with the biophysical and socioeconomic conditionsof the region.

Rainwater harvesting agriculture (RHA) based on the inclu-sion of rainwater harvesting techniques may offer a solution.RHA is an integrated system for water management on rainfedland in semiarid areas. This system can help farmers to allevi-ate water constraints. The RHA system consists of a synergeticcombination of different technological components including arainwater harvesting system, a water-saving irrigation system,and a highly effective crop production system. Among these 3components, the rainwater harvesting system is the core, its func-tion is to provide water for domestic and agricultural needs. Aneffective water-saving irrigation system is crucial for the eco-nomical and effective use of water.

Scientists in China have developed a wide variety of simple,

low-cost mobile and semi-fixed micro-drip irrigation systemsthat are suitable for small-scale farmers (25). However, onlythrough integration of the components can the expected objec-tive of agricultural water management be achieved.

The rainwater harvesting system consists mainly of collectionsurface, runoff channel, sediment tank and storage container (Fig.2). Collection surfaces can be waterproofed by compacted dirt,melted wax, asphalt, concrete, and plastic films and the like.They are usually built in courtyards for household use and sur-rounding or above agricultural fields for irrigation purposes. Inmany areas, roofs, courtyards, rocky hillsides, and asphalt roadsare used as collection surfaces. Containers for the storage of rain-water include wells, tanks, mini-reservoirs etc. In the loess ar-eas the most common storage containers are wells. There are twobasic types of the wells, namely traditional earthen wells and

Figure 2. A schematicdiagram showing thesmall-scale rainwaterharvesting systembeing widely used byhousehold farmers insemiarid areas ofGansu province.

Rainwater storage wells with concrete collection surfaces for irrigation,Yuzhong County, Gansu Province, July 1997. Photo: S. Cook.

Manual water pump


Sediment tank

Runoff channel

Collection surfaceWater intake

Concrete well wall

Main pipe

Lateral lineValve


Well cover



Well bottom

20 cm

450 cm

470 cm




80 c


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tensive mountainous and hilly topography of the semiarid areas.(ii) The small scale of this system makes it easy to construct,operate and manage at the small farm level, which is the basicunit of agricultural production in China today. (iii) The owner-ship of rainwater harvesting facilities such as collection surfacesand storage wells belong to individual households and the farm-ers have a greater incentive to maintain them. (iv) Unlike large-scale water development projects, this small-scale system doesnot require long construction delays, and can provide benefitsthe same year they are begun. (v) The construction of small-scale rainwater harvesting systems requires relatively low invest-ments and is more affordable to farmers in poor areas. For in-stance, the average cost (including labor and material inputs) forbuilding a 30 m3 concrete well is RMB 1250 yuan (about USD125), because of the low cost of labor in China. When compari-son is made on a per unit irrigated area basis, the average costof small-scale rainwater harvesting systems amounts to only 50–65% of that of conventional large-scale water developmentprojects (26).

The scale of the rainwater harvesting system to irrigate a smallfarm can be determined according to (i) the annual amount ofrunoff production per unit of catchment area, and (ii) the actualarea to be irrigated and the amount of irrigation water requiredper unit of irrigated area under limited irrigation conditions. Theannual amount of runoff production per unit of catchment areain a given area can be estimated by the following formula:

Yw = Cr x Hp/1000 Eq. 1

where Yw is the annual amount of runoff production per unit ofcatchment area (m3 m–2); Cr is the runoff coefficient from a par-ticular collection surface; and Hp is the annual rainfall depth(mm) under different rainfall probabilities.

Because of the variability in rainfall, runoff coefficients ofthe collection surfaces vary with the characteristics of rainfall.Table 3 presents the annual average values of runoff coefficientsfor different collection surfaces. The data in the Table are froma 4-year runoff plot study conducted by a research team fromthe Gansu Water Conservancy Science Institute (27). In thisstudy, researchers observed the runoff coefficients of 9 differ-ent collection surfaces over 600 different rainfall events (vary-ing intensities, depths, and antecedent moisture content) in sev-eral representative sites of the semiarid areas of Gansu province.Given crops to be irrigated, their annual amount of irrigation

water requirements per unit of irrigated area can be determinedusing the following formula:

Iq = (Rw – 10Pe – Ws)/η Eq. 2

where Iq is the annual amount of irrigation water requirements(m3 ha–1); Rw is crop water requirements for full yield, namelypotential evapotranspiration (m3), which can be calculated by amodified Penman equation (28); Pe is the rainfall during the cropgrowing season (mm); Ws is the available water storage in thesoil before planting (mm), which can be determined accordingto field experiments or can be roughly estimated based on(0.15~0.25) Rw in the absence of field data; and η is the factorof water use and its values can be set 0.8~0.9 when drip irriga-tion system is used.

According to field studies, using a drip irrigation system it ispossible in semiarid environments, to irrigate crops such asspring or winter wheat 2 to 3 times during the whole growingseason, with a water quantity of 150–225 m3 ha–1 for each pe-riod. At this level of supplemental irrigation, irrigated crops canproduce an average of 20–40% more yield than unirrigated crops(29–31).

Effects of RHA Practices on Improving AgriculturalProductionAs part of a long-term research effort aimed at establishing aproductive, sustainable RHA system in the semiarid areas ofChina, a series of field studies has been carried out in a jointresearch project between Lanzhou University and the Instituteof Dryland Farming in Gansu Academy of Agricultural Sciences,in several counties of the Gansu province (29, 30). The effectsof RHA in improving production can be illustrated using Dingxicounty as a case study. In 1993, field research was conductedin the Dingxi Agricultural Experimental Station. Long-term(1960–1990) average climatic data for the study area are 415 mmrainfall, 6.2°C mean temperature, 1432 mm open-pan evapora-tion and a frost-free period of 140 days. For the year of the study,annual rainfall was 420 mm, close to the 30-year average, andthe rainfall during the crop growing season was 289 mm, i.e.slightly higher than the 30-year average (279 mm). Hence, thisstudy can be considered representative for long-term averages.Spring wheat (Triticum aestivum, cv. Longchun 8139-2) wasplanted at a seeding rate of 225 kg ha–1 in late March. The plotsize was 2.6 m . 5 m with a 1.2 m space between plots. Plots

Rainwater storage wells with plastic collection surfaces for irrigation, Dingxi County,Gansu Province, June 1997. Photo: S. Cook.

modern concrete wells. Wells have vari-ous shapes such as vase-like, ball-likeand column-like. Earthen wells are usu-ally built by digging into the ground,combined with special treatment usingcement or red clay soil to prevent seep-age loss. To prevent evaporation loss, afinished well often has a concrete cover.Geohydrological research suggests thatin the loess regions the optimal volumeof an earthen well is 15–20 m3, and theoptimal volume of the concrete wells is30–50 m3 (15). However, in some rockymountainous areas like Weihui county ofHenan province in central China, somelarger wells, the so-called ‘water cave’,with a volume of over 500 m3 are builtby digging into rocky cliff sides. Theselarge wells are suitable for flood waterscollected during intense rainstorms.Compared with large-scale water devel-opment projects the rainwater harvestingsystem shows the following superiorqualities. (i) It is well suited to the ex-

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were arranged as a randomized complete block with 3 replica-tions. Because the soil of this area is naturally rich in K and de-ficient in N and P, farm manure was extensively applied to theexperimental plots prior to planting. In addition, according to soiltest recommendations, adequate amounts of chemical fertilizer(bi-ammonium phosphate and urea) were applied at seedingdepth to provide 90 kg N and 60 kg P2O5 ha–1. The experimentincluded 3 irrigation treatments: namely irrigating once in theheading stage, twice in the tillering and heading stages and threetimes in the tillering, jointing, and heading stages. Nonirrigatedspring wheat served as a control. In each treatment, the amountof water supplied to the crop was approximately 350 m3 ha–1.This study shows that average yields of spring wheat irrigatedfor one, two and three times were 4.70, 5.02 and 5.49 Mg ha–1,respectively, i.e. 28, 37 and 50% higher than the control (3.66Mg ha–1). The water supply efficiency, defined as yield incre-ment per unit of water supplied, of the 3 treatments averaged2.97, 1.94 and 1.74 kg m–3, respectively.

In another study at the same site, 4 improved cultivars of corn(Zea mays) including Lindan 160, Lindan 141, Jiudan 3 andDanyu 13 were planted in rows (with a population of 60␣ 000ha–1) in late April under the plastic film mulch condition. Ad-equate amounts of fertilizers N and P were applied to the ex-perimental plots according to soil test recommendations. All thecultivars received supplemental irrigation of about 750 m3 ha–1

during the earring stage (a most sensitive period to water stress),with a nonirrigated control. The 297 mm rainfall occurred dur-ing the corn growing season. This study indicates that the aver-age yields of irrigated cultivars were 9.05 (Lindan 160), 8.90(Lindan 141), 8.58 (Jiudan 3) and 7.00 Mg ha–1 (Danyu 13), i.e.88, 31, 34 and 20% higher than the nonirrigated cultivars. Thewater supply efficiencies of the 4 cultivars averaged 6.20 (Lindan160), 2.83 (Lindan 141), 2.91 (Jiudan 3) and 1.53 kg m–3 (Danyu13). Furthermore, a field study involved in supplemental irriga-tion of rainfed fruit trees was also carried out at the same site.In this study, 3 cultivars of pear (Pyrus spp.) including Zaoshu,Jinfeng and Korea Yangli were used. For each cultivar, 3 same-sized, 5-year-old pear trees were chosen as a cohort with 3 rep-licates. All pear trees were irrigated 4 times using the sub-surface drip irrigation during the period from flowering to fruit

expanding stages, with a nonirrigated control. Each time, theamount of water supplied was 15 kg tree–1, about 60 kg tree–1 intotal. This study shows that the average fruit yields per tree forthe 3 irrigated cultivars were 26.2 (Zaoshu), 34.4 (Jinfeng) and23.6 kg (Korea Yangli), with increases of 58, 83 and 102% ascompared with nonirrigated trees. The average water supplyefficiencies of the 3 cultivars were 0.16 (Zaoshu), 0.26 (Jinfeng)and 0.20 kg kg–1 (Korea Yangli), respectively. At the same time,irrigation treatments significantly improved the quality of thefruit. All these data suggest that implementing RHA practicescan improve performance in rainfed farming systems in semiaridareas.

Environmental Benefits of RHA PracticesProblems of environmental degradation, particularly soil erosionin China’s semiarid areas has received a great deal of attentionboth nationally and internationally (32–34). These problems havea biophysical root cause related to the climatic, topographic andgeological features of the region, which combine to produce anerosion-prone landscape (35). However, soil erosion is closelytied to poor land-use management. Since the beginning of thecentury, particularly over the last several decades, rapidly grow-ing human population has placed severe pressure on productivesoil resources, thus leading to a rapid decline in the average percapita cultivated land in the region. In the case of Gansu prov-ince, its total population has increased from about 11.4 mill. inthe early 1950s to 25. 6 mill. in the late 1990s, with an averagegrowth of over 320␣ 000 persons every year. As a result, the av-erage per capita cultivated land has decreased from approxi-mately 0.4 ha in the early 1950s to less than 0.2 ha in the late1990s. To meet the increasing food needs resulting from popu-lation growth, a considerable increase in food and fiber produc-tion will be needed. Under these conditions, farmers were forcedto convert more and more forestland and grassland into croplandand at the same time to increase cultivation of steep erodibleslopes in order to obtain an adequate harvest. Consequently, thishas caused the increase in the scale and severity of soil erosionand a reduction in soil fertility, which are major factors affect-ing the sustainability of agricultural system. It is estimated thatabout 75% of the Loess Plateau in China has been severely af-

Table 3. Average annual values of runoff coefficients (%) for the 9 different collection surfacesunder different annual rainfall and rainfall probabilities (%).

Average Different collection surfacesrainfall(mm) Probability

(%) T1 T2 T3 T4 T5 T6 T7 T8 T9

50 80 75 50 40 53 25 46 68 8(40) (38) (25) (20) (27) (13) (23) (34) (4)

400~500 75 79 74 48 38 25 23 45 67 7(39) (37) (24) (19) (23) (12) (23) (34) (4)

90 76 69 39 31 41 19 36 65 6(38) (35) (20) (16) (21) (10) (18) (33) (3)

50 80 75 49 40 52 26 46 68 8(32) (30) (20) (16) (21) (10) (18) (27) (3)

300~400 75 78 72 42 34 46 21 41 66 7(31) (29) (17) (14 (18) (8) (16) (26) (3)

90 75 67 37 29 40 17 34 64 5(30) (27) (15) (12) (16) (7) (14) (26) (2)

50 78 71 41 34 47 20 41 66 6(24) (21) (12) (34) (14) (6) (12) (20) (2)

200~300 75 75 66 34 28 40 17 34 64 5(23) (20) (10) (28) (12) (5) (10) (19) (2)

90 73 62 30 24 33 13 28 62 4(22) (19) (9) (24) (10) (4) (8) (19) (1)

T1–Concrete; T2–Cement tile; T3–Machine-made brick tile; T4–Traditional brick tile; T5–Compacted surface of mixed red clay andloess soil; T6–Compacted surface of loess soil; T7–Gravel-covered plastic film; T8–Asphalt road; T9–Untreated (natural) loess soilsurface. The values in parentheses are the annual amount of runoff production per unit of catchment area (m3 100 m–2) with 9 differentcollection surfaces.

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fected by soil erosion (36). Each year nearly 1600 mill. tonnes(Mt) of topsoil are lost from the region through water and winderosion, with associated loss of about 8 Mt of organic matter,2.4 Mt of nitrogen, 3.2 Mt of potassium and 0.02 Mt of avail-able phosphorus (37). The severity of this situation becomes ap-parent when it is recognized that soil is formed only at approxi-mately 1 t ha–1 yr–1 (38). To combat erosion and agricultural soildegradation, both the central and regional governments have for-mulated a series of policies to prohibit cultivation of steep slopes,particularly slopes steeper than 25° (39). However, this limit isoften breached, and the cultivation of steep slopes is still goingon in many areas. An important cause for this is the low andunstable productivity in rainfed land. This leaves farmers withno choice other than to put more sloping lands into production.It is evident that the key to prevent soil erosion is to stop culti-vation of steep slopes, whereas the key to stop this cultivationis to increase agricultural productivity in existing rainfed flat andterraced fields by developing and adopting more effective wa-ter management practices (40).

RHA has the potential to prevent soil erosion in two ways.(i) RHA is in itself a useful measure in soil and water conserva-tion, by capturing and storing runoff during heavy rainstorms,it can directly contribute to the reduction of soil and water ero-sion. Studies show that over 70% of the soil erosion that occursin the semiarid mountainous and hilly areas is caused by a fewintense rainstorm events (41). (ii) RHA is also an effective yield-increasing practice, by implementing supplemental irrigation tocrops, it can significantly increase productivity of rainfed landbecause of improved availability of water. While increased pro-ductivity in flat and terraced fields can help reduce the incen-tives that farmers have to cultivate steep slopes as an insurancestrategy against crop failure. Taken out of grain production, slop-ing lands can be used to develop protective economic forest orgrassland production. This not only provides a far better soilcover than grain crops, but it is also beneficial to the adjustmentof the structure of agriculture, decreasing the production of sin-gle cereal crops and increasing the production of livestock. Arecent survey study in several selected villages which haveadopted RHA practices, in Dingxi and Yuzhong counties ofGansu province, shows that adoption of RHA practices can re-ally help decrease the incentives that local farmers have to cul-tivate fragile sloping lands (42). A significant change is that moreand more villagers in these villages have already started to giveup the cultivation of steep slopes because they have been ableto produce adequate grains to meet their practical needs simplyby cultivating more productive flat and terraced fields. Some vil-lagers use these retired sloping lands to grow either perenniallegumes for animal feed or economic trees for market sales, thus,increasing cash income and the standard of living for the vil-lagers.

SUCCESSFUL IMPLEMENTATION OF RHA INGANSU PROVINCERHA was first practiced in Gansu. Since 1995, RHA has beenpromoted by the authority as a ‘solution’ to the problem of wa-ter shortages, thus leading to a rapid development of RHA inthe province. In order to bring about a massive application ofthis technology, the Gansu provincial government launched aprogram, the so-called 1-2-1 system, in 1995. Initially, the pri-mary focus of the program was the central parts of the province,an area with the most serious water shortages. This program builtupon prior success in fulfilling household domestic and produc-tive requirements for water on an experimental scale. Its pur-pose is to help each household farmer build about 100 m2 con-crete collection surfaces, two concrete storage wells and irrigateone mu (1/15 ha) of cropland for production of high market valuecash crops (e.g. vegetables). In this program, the government

provided farmers with materials (e.g. steel and cement) for build-ing the collection surfaces and storage wells and necessary tech-nical services, whereas farmers contributed the labor. In addi-tion, the farmers involved in the program can also obtain finan-cial support in the form of microcredits from the ongoing UNDP-assisted projects in the province. After implementation of thisprogram for 3-years there are already significant changes. Theconsequences are that approximately 22 mill. m2 collection sur-faces and 9.1 mill. storage wells have been constructed, supply-ing 1.31 mill. rural residents and 1.2 mill. livestock adequate sup-plies of drinking water. At the same time, some 2.1 mill. mu(about 140␣ 000 ha) of rainfed lands have been irrigated usingrainwater harvesting (43). The positive experience gained fromthis program so far encouraged the Gansu provincial governmentto project expansion of the program in 1998. The new programcovered the whole semiarid area of the province, the goal beingto help each rural household in the project areas irrigate 3 mu(0.2 ha) of cropland using the rainwater harvesting system overa 5-year period. The program has already made some progress.

The success of RHA in Gansu province has had a profoundimpact on other provinces in northwest China. Over the last fewyears, RHA has been introduced in neighboring provinces suchas Ningxia, Shanxi, Shannxi, and Inner Mongolia, as well as inthe central parts of China such as Hebei and Henan provinces(43). In these provinces, some programs similar to the 1-2-1 sys-tem in Gansu province have been launched by local govern-ments, leading to the rapid spread of RHA over a wider rangeof arid, semiarid and drought-prone sub-humid regions. A grow-ing number of farmers have benefitted from the use of this tech-nology. Currently, 4 basic types of agricultural production basedon the inclusion of rainwater harvesting systems are beingpracticed by household farmers in China’s semiarid areas: (i)semi-intensively managed field food crops (e.g. wheat, corn andpotatoes); (ii) semi-intensively managed field cash crops (e.g.oilseed, sugar beet, tobacco and water melon); (iii) semi-inten-sively managed fruit trees (e.g. pear, apple, peach and grape);and (iv) intensively managed high market value crops grown ingreenhouses (e.g. vegetables, Chinese medicinal plants and flow-ers).

CONCLUSIONSConventional rainfed farming in China’s semiarid areas is fac-ing serious resource (especially water resource) and environmen-tal (especially soil erosion) problems. The solution to these prob-lems depends largely on the development of more effective wa-ter-management practices. Research so far on RHA systems hassuggested that RHA is a rapid, effective and inexpensive ap-proach to water management on rainfed land in semiarid areaswith unreliable rainfall. RHA has the potential to improve per-formance in rainfed farming systems and to address environmen-tal problems. Hence, from the perspective of sustainable devel-opment in agriculture, developing and adopting RHA is essen-tial to achieving a productive, sustainable rainfed agriculture inChina’s semiarid areas.

However, to be successful, the RHA system needs to be inte-grated with a comprehensive agricultural management system.This means that the management of RHA should be combinedwith other agricultural technologies and management practicesincluding water and conservation measures, crop management,and soil fertility management, as well as the selection of suit-able crop varieties such as drought-tolerant crops and salinity-tolerant crops. In addition, with the exception of the use of natu-ral precipitation, other nonconventional water resources includ-ing saline/brackish water and treated wastewater can be used aspotential water sources for agricultural purposes in semiarid ar-eas in the future. Moreover, the spread of RHA in different re-gions also requires consideration of a range of technological, bio-

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References and Notes1. Frasier, G.W. 1985. Technical economic and social considerations of water harvesting

and runoff farming. In: Arid Lands: Today and Tomorrow, International Research andDevelopment Conference. Whitehead, E.E. et al. (eds). Tucson, Arizona, USA, Octo-ber 20–25, 1985, XIX+1435 pp.

2. Lavee, H., Poesen, H. and Yair, A. 1997. Evidence of high efficiency water-harvest-ing by ancient farmers in the Negev Desert, Israel. J. Arid Environ. 35, 341–348.

3. Richards, K.S. 1972. Rainwater harvesting for domestic purposes. Rhodesia Agric. J.Technol. Bull. 15, 45–51.

4. Boers, M.T. and Ben Asher, J. 1982. A review of rainwater harvesting. Agric. WaterMgmt 5, 145–170.

5. Sheikh, M.I., Shan, B.H. and Aleem, A. 1984. Effect of rainwater harvesting methodson the establishment of tree species. Forest Products J. 8, 257–264.

6. Boers, T.M., Zondervan, K. and Asher, B. 1986. Micro-catchment-water-harvesting forarid zone development. Agric. Water Mgmt 12, 21–39.

7. Alcock, P.G. and Verster, E. 1987. Investigation into unconventional sources of waterfor a periurban-rural district of Kwazulu South Africa. South Africa J. Sci. 83, 348–352.

8. Cater, D.C. and Miller, S. 1991. Three years experience with an on-farm macro-catchment water harvesting system in Botswana. Agric. Water Mgmt 19, 191–204.

9. Shah, B.H. 1992. Development of agroforestry model using water harvesting systemin semi-arid and arid zones. Pakistan J. Forestry 42, 190–199.

10. Kronen, M. 1994. Water harvesting and conservation techniques for smallholder cropproduction systems. Soil Tillage Res. 32, 71–86.

11. Tabor, J.A. 1995. Improving crop in the Sahel by means of water-harvesting. J. AridEnviron.30, 83–106.

12. Kaarakka, V. 1996. Management of bushland vegetation using rainwater harvesting ineastern Kenya. Acta Forest. Fenn. 253, 2–93.

13. Rockström, J. and Valentic, C. 1997. Hillslope dynamics of on-farm generation of sur-face water flows: The case of rainfed cultivation of pearl millet on sandy soil in theSahel. Agric. Water Mgmt 33, 183–210.

14. Agarwal, A. and Narain, S. 1997. Dying wisdom: The decline and revival of tradi-tional water harvesting systems in India. The Ecologist 27, 112–116.

15. Zhao, S.L. 1996. An Introduction to Catchment Agriculture. Shannxi Sci. Technol.Press, Xian. (In Chinese).

16. Zhu, X.M. 1989. Soils in the Loess Plateau and Agriculture. China Agric. Press, Beijing.(In Chinese, summary in English).

17. Shan, L. and Cheng, G.L. 1993. Theory and Practice of Dryland Farming in the LoessPlateau of China. China Sci. Press, Beijing. (In Chinese).

18. Wei, H., Zhao, S.L. and Wu, G.H. 1996. Meteorological aspects of rainwater harvest-ing agriculture in the semi-arid loess plateau. J. Arid Land Resources Environ. 10, 64–70. (In Chinese, summary in English).

19. Li, F.R. 1998. Studies on Arid Agricultural Ecosystems. Shannxi Sci. Technol. Press,Xian. (In Chinese, summary in English).

20. Li, F.R., Zhao, S.L. and Geballe, G.T. 2000. Water use patterns and agronomic per-formance for some cropping systems with and without fallow crops in a semi-arid en-vironment of northwest China. Agric. Ecosyst. Environ. 79, 129–142.

21. Lu, Z.F. and Zhao, G.S. 1991. Soil-water conserving farming and its yield-increasingtechnical systems. China. J. Soil Water Cons. 5, 166–171. (In Chinese, summary inEnglish).

22. Shan, L. 1998. Technological measures for sustainable dryland farming in the semi-arid regions of China. China Science Daily (Overseas Edition), Zhongguo KexuebaoPublishing House, January 25. (In Chinese).

23. Yang, Q.Y. 1990. The characteristics of water deficits for certain grain crops in theloess plateau and the problems of rainfed agriculture. China J. Natural Resources 1,24–31. (In Chinese, summary in English).

24. Zhao, S.L., Wang, J. and Li, F.M. 1995. Limitations of soil-water conserving farmingin the semi-arid loess plateau. Acta Bot. Boreal. Occident Sin. 15, 1–7. (In Chinese,summary in English).

25. Wu, F.X. 1995. Engineering design of rainwater harvesting systems. Gansu WaterConserv. Water-Electricity Technol. 4, 34–39. (In Chinese).

26. Zhang, Z.X., Gong, S.H. and Wang, X. L. (eds). 1999. Rainwater Harvesting Engi-neering Technologies. China Water Conserv. Water-Electricity Press, Beijing, pp. 50–66.

27. The research term by the Gansu Provincial Water Conservancy Science Institute 1990.Field Studies on the use of rainwater in arid and semi-arid areas of Gansu province.Gansu Water Conserv. Water-Electricity Technol. (special issue). (In Chinese).

28. Pei, B.X. 1989. Measurement and Calculation of Evaporation and Evapotranspiration.Meterol. Publishing House, Beijing, pp. 598–638. (In Chinese).

29. Li, F.M., Zhao, S.L., Duan, S.S., Gao, S.M. and Feng, B. 1995. Preliminary study onlimited irrigation for spring wheat field in semi-arid loess region of China. China J.Appl. Ecol. 6, 259–264. (In Chinese, summary in English).

30. Gao, S.M. and Zhu, R.S. 1996. Effects of supplemental irrigation and plastic film mulch-ing on yields of rainfed crops. J. Arid Land Resources Environ. 2, 42–48. (InChinese,summary in English).

31. Ren, Z. X., Bi, J.T. and Gu, Y.T. 1998. Research and application of well-based rain-water harvesting systems in arid mountain area of Ningxia province. J. Arid Land Re-sources Environ. 12, 58–63. (In Chinese, summary in English).

32. Robinson, A.R. 1981. Erosion and sediment control in China’s Yellow River basin. J.Soil Water Cons. 36, 125–127.

33. Lee, H. 1984. Soil conservation in China’s loess plateau. J. Soil Water Cons. 39, 306–307.

34. Wen, D.Z. 1993. Soil erosion and conservation in China. In: World Soil Erosion andConservation. Pimentel, D. (ed.). Cambridge University Press, Cambridge, pp. 63–85.

35. Jing, K. 1988. A study on the relationship between soil erosion and the geographicalenvironment in the Middle Yellow River basin. J.Arid Land Resources Environ. 1, 289–299. (In Chinese, summary in English).

36. Zhang, Z.H. 1992. Grassland agriculture and its technical systems. In: Proc. Int. Con.on Agroecosystems in the Loess Plateau. Ren, J.Z. (ed.).Gansu Sci. Technol. Press,Lanzhou, pp. 37–42. (In Chinese, summary in English).

37. Ren, J.Z. 1992. Ecological productivity of grassland farming system on the Loess Pla-teau of China. In: Ren, J.Z. (ed.). Proc. Int. Conf. on Agroecosystems in the Loess Pla-teau. Gansu Sci. Technol. Press, Lanzhou, pp. 37-42. (In Chinese, summary in Eng-lish).

38. Pimentel, D. (ed.) 1992. World Soil Erosion and Conservation. Cambridge UniversityPress.

39. The Gansu Provincial Commission of Science and Technology 1994. A Guideline ofthe Gansu Agrotechnological Policies. Gansu Sci. Technol. Press, Lanzhou, pp. 3–9.(In Chinese).

40. Li, F.R. and Li, S.J. 1998. A choice of strategy for sustainable development of rainfedfarming in water-limiting areas of northwest China. In: The 1st Annual Symposium ofthe National Soft Science Research in China. China Sci. Technol. Press, Beijing, pp.876–886. (In Chinese).

41. Li, S.K. 1992. On Harnessing Sloping Lands in Eroded Areas in the Middle Reachesof the Yellow River. Gansu Sci.Technol. Press, Lanzhou. (In Chinese).

42. Wei, H.L., Bai, J.M. and Yang, X.T. 1998. Analysis of benefits of water-harvestingfarming in semi-arid loess areas. J. Arid Land Resources Environ. 12, 41–47. (In Chi-nese, summary in English).

43. Yang, A.M. 1998. Practice of Rainwater Harvesting Systems in Gansu province. In:The Challenges and Strategies for Development of Rainfed Agriculture in Semi-AridRegions. Xu, J. (ed.). Lanzhou University Press, Lanzhou, pp. 308–312. (In Chinese).

44. Giampietro, M. 1997. Exploring the link between technology, natural resources andsocioeconomic structure of human society: A theoretical model. In: Adv. Human Ecol.Vol. 6. Freese, L. (ed.). JAI Press, Greenwich CT, pp. 73–128.

45. This research was supported by a special President’s fund from the Chinese Academyof Sciences and the visiting scholar foundation from the State Key Laboratory of AridAgroecology in Lanzhou University.

46. First submitted 20 Aug. 1999. Accepted for publication after revision 11 April 2000.

Li Fengrui is professor in agroecology at the Department ofEcology and Agriculture in the Cold and Arid RegionsEnvironmental and Engineering Research Institute,Academia Sinica. His address: Engineering ResearchInstitute Academia Sinica, 260 Donggang West Road,Lanzhou 730000, PR China.E-mail: [email protected]

Seth Cook is a PhD student in environmental studies at theSchool of Forestry and Environmental Studies in YaleUniversity.E-mail: [email protected]

Gordon T. Geballe is professor and Associate Dean of theSchool of Forestry and Environmental Studies in YaleUniversity.E-mail: [email protected]

William R. Burch, Jr. is Hixon Professor in natural resourcemanagement at the School of Forestry and EnvironmentalStudies in Yale University.E-mail: [email protected]

Their address: Yale School of Forestry and EnvironmentalStudies, 205 Prospect Street, New Haven, CT 06511, USA.

physical, geohydrological, ecological, social, cultural, economic,and political factors, especially the presence of tremendous het-erogeneity among different regions. On the whole, the successof RHA is likely to hinge upon: (i) whether research scientistsand extension agents can provide long-term training and tech-nical services to local farmers, thereby, increasing their abilityto apply the technology and to ensure adequate maintenance ofrainwater harvesting facilities; (ii) the need to develop a widevariety of rainwater harvesting technologies that are ecologicallysound and economically viable as alternatives for farmers; (iii)the need to design and develop alternative policy instruments andimplementing strategies that facilitate the spread of RHA. It haslong been recognized that there are interactive forward and back-ward linkages between technology, infrastructure and institu-tional structures (44). In many cases, technological innovationsin the agricultural sector often fail to be widely applied, largely

due to the organizational and/or institutional incompatibilityrather than technological complexity. When the use of RHA isexpanded from a household level to a village level and to a wa-tershed scale, it not only requires technological development butalso entails parallel development of social institutions and man-agement systems in order to ensure an equitable allocation andefficient use of water, soil, and other resources.

As with any agricultural technology, the effects of RHA arelikely to be complex and ambiguous. Therefore, further researchis needed to assess the ecological, social and economic impactsof RHA from a plurality of perspectives in a wide range of dif-ferent localities. This study can contribute to a better understand-ing of the complex RHA system, which may help in the discus-sion of trade-offs related to sustainability of this agrosystem. Thestudy may also help in applying RHA more effectively and inmitigating some of the potential problems.