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Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
1
Title 1
Changes and uncertainties in the vegetation and terrestrial water cycle of Mesoamerica under 2
climate change scenarios 3
Authors 4
Pablo Imbach1*
(corresponding author), Luis Molina1, Bruno Locatelli
2, Olivier Roupsard
1,3, Gil 5
Mahé4, Ronald Neilson
5, Lenin Corrales
6, Philippe Ciais
7 6
Contact details 7
1Climate Change Program, CATIE, Costa Rica;
2CIRAD UPR Forest Ecosystem Services, 8
Montpellier, France; CIFOR ENV Program, Bogor, Indonesia; 3CIRAD-Persyst, UPR80, 9
Fonctionnement et Pilotage des Ecosystèmes de Plantations, Montpellier, France; 4 10
IRD/HydroSciences Montpellier, Case MSE, Université Montpellier 2, 34095 Montpellier, 11
Cedex 5, France; 5USDA Forest Service, Pacific Northwest Research Station in Corvallis, 12
Oregon, USA; 6Apdo. 299-11001, San José-Costa Rica;
7IPSL – LSCE, CEA CNRS UVSQ, 13
Centre d’Etudes Orme des Merisiers, 91191 Gif sur Yvette, France. 14
Dateline: 15
*CATIE 7170, Turrialba, Cartago 30501, Costa Rica. E-mail: [email protected] 16
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Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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ABSTRACT 22
We aimed at evaluating the likelihood of the impacts of climate change on potential 23
vegetation and the water cycle in Mesoamerica to support future development of ecosystem 24
based adaptation strategies. Mesoamerica is a global biodiversity hotspot with highly diverse 25
topographic and climatic conditions and is among the tropical regions with the highest expected 26
changes in precipitation and temperature under future climate scenarios. We used the 27
biogeographic soil-vegetation-atmosphere model MAPSS for simulating the integrated changes 28
in leaf area index, vegetation life forms (grass, shrubs and trees), evapotranspiration, and runoff 29
at the end of the 21st century. We assessed the likelihood of changes in vegetation and water 30
cycle under 136 climate scenarios, generated with 23 general circulation models (GCMs) and 31
belonging to three groups of greenhouse gas emission scenarios (low, intermediate and high 32
emissions). Our results showed that potential vegetation will likely shift from humid to dry types 33
and LAI is likely to decrease over 77 – 89% of the region, depending on climate scenario groups. 34
Runoff will decrease across the region even in areas where precipitation increases, as 35
temperature change will increase evapotranspiration. Higher emission scenarios show lower 36
uncertainty in modeled impacts. Although uncertainty is high for future precipitation, the impacts 37
of climate change on vegetation and water cycle are predicted with relatively low uncertainty. 38
Projected climate change will reduce ecosystems leaf area and water balance with large 39
consequences for biodiversity and ecosystem functioning. Future expansion of dry ecosystems 40
indicates that conservation efforts should consider current dry ecosystems as a source of genes 41
and species to facilitate adaptation of ecosystems to climate change while seeking potential 42
refugees for the threatened humid ecosystems. 43
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
3
Keywords Central America, ecosystem services, adaptation to climate change, biodiversity, 44
protected areas, freshwater, biomass 45
1. Introduction 46
There is a need to understand the potential impacts of climate change on ecological systems 47
before defining adaptation measures for ecosystems and the people who depend on their services 48
(Millenium Ecosystem Assessment 2005). The Mesoamerican region, where approximately 60 49
million people depend highly on natural resources, is a global biodiversity hotspot (DeClerck et 50
al. 2010), with more than 5000 endemic vascular plant species (Greenheck 2002). It is a reservoir 51
of the evolutionary history of biodiversity (Sechrest et al. 2002) and a bridge between North and 52
South America for mammals (MacFadden 2006), birds (Weir et al. 2009), and plants (Gentry 53
1982). Countries in the region have developed national and regional policies for integrating 54
biodiversity conservation and development (e.g., the Central American System of Protected 55
Areas1 and the Puebla-Panama plan
2) that should account for future climate threats to help 56
reduce the vulnerability of the region. 57
Central America could be the tropical region most exposed to climate change (Giorgi 2006). 58
Between 1961 and 2003, temperatures have been increasing and precipitation has been 59
intensifying, with a larger amount of annual precipitation falling during extreme events (Aguilar 60
et al. 2005). Observed trends in annual rainfall differ on signal (positive or negative) and 61
statistical significance depending on the data source used. Aguilar et al. (2005) found a non-62
significant trend based on weather station data while Malhi & Wright (2004) found significant 63
increases in some areas based on spatial interpolation of weather station data over forest covered 64
1 http://www.sica.int/
2 http://www.planpuebla-panama.org/
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
4
areas. Furthermore, Neelin et al. (2006) found an observed decrease in precipitation trends based 65
on remote sensing sources (except for southern Panama that shows the opposite trend), but 66
highlights the difficulty of discerning the natural multi-decadal or inter-annual variability on 67
these observed trends in tropical areas. Precipitation is projected to decrease in the future (Neelin 68
et al. 2006) but uncertainties remain on this development since the year at which the trend for 69
each model is discernible from natural variability and at which several models agree on the trend 70
is highly variable. However, the potential for extreme droughts in the region is becoming 71
increasingly clear (Dai 2010). The impacts of these changes in climate on vegetation and 72
hydrology will affect the availability of natural resources (i.e. water and biomass) with 73
implications for development. For example, the collapse of the Mayan civilization in Northern 74
Mesoamerica, has been linked to multi-decadal droughts and its impact on resource availability 75
(Curtis et al. 1996; Haug et al. 2003). 76
The impacts of climate change on ecosystems depend on non-linear and complex interactions 77
among soils, vegetation, and climate. These interactions can be simulated by process-based 78
models, such as land surface models, which functionally integrate atmospheric, vegetation and 79
hydrologic responses that cannot be accomplished by correlative climate-vegetation models 80
(Yates et al. 2000) and have been applied to modelling the impacts of climate change on 81
vegetation and hydrology for all IPCC reports since 1995 (e.g., Cramer et al. 2001; Neilson; 82
Marks 1994). 83
Uncertainties of impacts are related to model structure, model parameters and input data, 84
including future changes in climate (IPCC 2005). Assessing uncertainties is crucial for informed 85
decision making and can be done using several ecosystem models, General Circulation Models 86
(GCMs), and emission scenarios. Calibrating and validating ecosystem models with past 87
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
5
observations allows the uncertainties arising from the ecosystem model to be analyzed and 88
reduced; however, uncertainties from climate scenarios cannot be diminished since the future 89
will never be precisely predictable. 90
We aimed to assess the impacts of climate change on vegetation and the water cycle in 91
Mesoamerica using the process-based Mapped Atmosphere Plant Soil System (MAPSS) 92
biogeography model (Neilson, 1995) with 136 climate scenarios downscaled from the outputs of 93
23 global GCMs under low (B1), intermediate (A1B) and high (A2) emission scenarios for the 94
2070-2099 period and applied in the IPCC 4th
assessment report. This allowed us to quantify the 95
magnitude and uncertainties of climate change impacts on vegetation life forms, leaf area index 96
(LAI), runoff and evapotranspiration. Due to the complex topography and spatial climate 97
variability in the region, we assessed the impacts at 1 km resolution. 98
2. Materials and methods 99
a. Study area: climate and vegetation 100
The study area spans a one million square kilometer area of land between 76.5 and 99 101
degrees longitude W and 6.5 and 22 degrees latitude N (excluding the Caribbean islands). It 102
extends from Panama in the south to southern Mexico in the north across six other Central 103
American countries (Costa Rica, Nicaragua, Honduras, El Salvador, Guatemala and Belize). The 104
region is biophysically diverse with a topography marked by a mountain range that reaches over 105
4000 m.a.s.l. and runs close to the Pacific coast (Fig. 1). 106
Climate is tropical and rainfall follows a bimodal seasonal cycle with high inter-annual 107
variability (Magaña et al. 1999). In the Pacific watersheds and Yucatán, seasonal rainfall occurs 108
from May to October, whereas rainfall occurs year-round in the Atlantic watersheds with a 109
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
6
weaker bimodal seasonal cycle. Pristine areas are covered with savanna and dry forests in the 110
Pacific watershed and Yucatán, and evergreen forests in the Atlantic watershed. Around 42% of 111
the region is covered by crops and pastures, 57% by natural vegetation and 2% by urban areas 112
(DeClerck et al. 2010) (Fig. 1). 113
b. Modelling approach 114
MAPSS is an equilibrium biogeography model that simulates the long-term average water 115
balance and potential vegetation, given an average climate, based on water and energy 116
constraints (Neilson 1995). The model, described in detail by Neilson (1995), has been applied in 117
earlier studies for modeling runoff and vegetation patterns of the United States (Bachelet et al. 118
1998; Bishop et al. 1998), and assessing the impacts of climate change globally (Neilson 1993a; 119
Neilson; Marks 1994) and in North America (Bachelet et al. 2001; Neilson 1993a; Neilson; 120
Drapek 1998; Scott et al. 2002). MAPSS simulates equilibrium runoff, evapotranspiration, leaf 121
area index (LAI), and potential vegetation life forms (trees, shrubs and grasses) depending on 122
climate and soils. MAPSS is a General Vegetation Model (GVM), a relatively new class of 123
models based largely on the fundamental principle that vegetation will continue to amass leaf 124
area at a given location until it utilizes nearly all of the available soil moisture (Horton 1933). 125
The assumption that LAI and vegetation forms adjust according to soil drought allows the model 126
to search for an equilibrium of LAI, evapotranspiration and soil moisture depending on 127
temperature and precipitation. This equilibrium model does not account for transient changes, as 128
would a Dynamic GVM (DGVM) and, therefore, the modeled future vegetation and hydrology 129
represent the equilibrium that would exist if long-term future climate remained as during the 130
simulated period of 2070-2099. The use of an equilibrium GVM is preferred for this study, given 131
the very high spatial resolution and the large number of scenarios. All DGVMs operate under the 132
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
7
same water-balance constraint, but are always approaching that constraint under a constantly 133
changing climate. The use of a GVM allowed the exploration of a much greater range of 134
uncertainty among climate scenarios with a far greater resolution of the extremely high 135
complexity of Central American terrain. 136
MAPSS has been satisfactorily calibrated and validated in Mesoamerica with data on LAI 137
and runoff in 138 catchments (Imbach et al. 2010). Following other studies in tropical areas 138
(Hély et al. 2006), we ignored the effects of elevated atmospheric CO2 concentrations on 139
stomatal conductance, water use efficiency, water balance, and plant growth, because of the lack 140
of knowledge of these processes in tropical areas (Körner 2009) at ecosystem level (Norby; Luo 141
2004) and of the combined effects of elevated CO2 and temperature change (Hickler et al. 2008). 142
Furthermore, relative to changes in precipitation and temperature, these effects might be 143
relatively small (Chambers; Silver 2004; Körner; Arnone 1992). However, MAPSS has been run 144
globally with and without a direct CO2 effect, emulated by a 35% reduction in stomatal 145
conductance, based on literature available at the time (Neilson; Marks 1994). 146
c. Climate scenarios 147
We used climate change scenarios produced by World Climate Research Programme, 148
Coupled Model Intercomparison Project phase 3 (WCRP-CMIP3). The scenarios of this multi-149
model dataset, used in the IPCC Fourth Assessment Report, were downscaled to a 2.5 minute 150
resolution (around 5 km pixel) by The Nature Conservancy-California. The climatology dataset 151
includes 48, 52 and 36 scenarios for low (B1), intermediate (A1B) and High (A2) emission 152
scenarios respectively, from the IPCC-SRES. As in other similar studies (Hulme et al. 1999; 153
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
8
Scholze et al. 2006), climate scenarios were constructed by adding an interpolated GCM 154
anomaly to our reference climatology (1950-2000) at a 1 km resolution (Hijmans et al. 2005). 155
d. Uncertainty assessment 156
We evaluated the uncertainties of the changes in model outputs between the reference 157
period (1950-2000) and 2070-2099 (the period for the future climatology used). For LAI, runoff, 158
and evapotranspiration, we only considered changes larger than 20% in absolute value to be of 159
potentially large significance and lower changes as no-change scenarios (other thresholds were 160
explored; see supplementary material). For vegetation structure, we considered changes in the 161
dominant life form of the canopy, e.g., from tree to grass or vice versa. Using the terminology 162
recommended by the IPCC (2005), we considered that a change is very likely if it is observed in 163
more than 90% of the scenarios, ―likely‖ if 90> 66%, ―about as likely as not‖ from 33<66%, 164
―unlikely‖ 10< 33%, and ―very unlikely‖ < 10%. We mapped the likelihood of impacts using 165
multicolored maps (Scholze et al. 2006; Teuling et al. 2010). 166
3. Results 167
All climate scenarios forecasted temperature increases in Mesoamerica at the end of the 168
century varying from less than 2.5 °C (average B1 scenarios) to more than 3.5 °C in the 169
northwest part of the region (average A2 scenarios). Precipitation is projected to increase or 170
decrease depending on the location and the scenario (Fig. 2a), and the absolute changes increase 171
with higher emissions (Fig. 2b). On average among the scenarios with decreasing precipitation, 172
the projected change is from 4% to more than 20% (larger reductions are observed in dry areas). 173
Uncertainties are the lowest for the highest emission scenarios (A2 group of scenarios). The 174
trend in decreasing precipitation is more certain in the north of the region than in Panama and 175
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
9
Costa Rica (Fig. 2a), which stand between areas of decreasing precipitation in the north and 176
areas of increasing precipitation south of the study area, i.e. in South America. 177
a. Water cycle 178
Annual runoff is likely to decrease over 61–71% of the area for all emission scenarios (red areas 179
in Fig. 3a) and likely to increase in less than 1% (blue areas in Fig. 3a). Uncertainty in predicted 180
changes in runoff is less with higher emissions, as a likely decrease in runoff is observed in 181
larger areas under scenarios A2 than under the other scenarios. Uncertainties about runoff are 182
higher in the northwest of the region, where opposing trends are observed under different 183
scenarios (see purple areas in Fig. 3a). In most of the south (Costa Rica and Panama) runoff will 184
likely decrease (Fig.3a). It is very unlikely that runoff will change in central Honduras and parts 185
of southern Mexico (white areas in Fig. 3a). 186
Evapotranspiration is likely to increase in 18–22% of the area, particularly in Panama, Costa 187
Rica, El Salvador, and parts of central Guatemala (blue areas in Fig. 3b), and likely to decrease 188
in <1% of the area. No changes in evapotranspiration are observed in the north (white areas in 189
Fig. 3b). Uncertainty in the likelihood of change in evapotranspiration is higher in the northwest 190
(purple areas in Fig. 3b) than in the rest of the region. 191
b. Vegetation 192
LAI is likely to decrease over 77–89% of the area (red areas in Fig. 3c) depending on the 193
scenario and likely to increase over less than 2% of the area (green areas in Fig. 3c). In areas 194
with less certainty in LAI trends (e.g., in central Panama, Costa Rica, and Honduras; coastal 195
Yucatan, and the highlands of El Salvador, Mexico, Guatemala, and Mexico), the scenarios show 196
mixed responses in LAI to these changes in climate (yellow areas in Fig. 3c), as anticipated by 197
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
10
Neilson 1993b) for any areas of rapid change (ecotones). The decrease in LAI is generally driven 198
by a decrease in tree and grass LAI (red areas in Fig. 4a and c), except in some areas of Mexico 199
where the change affects shrub-dominant life forms (Fig. 4b). An increase in grass LAI (green 200
areas in Fig. 4c) is the driver of the increases in total LAI (green areas in Fig. 3c) in savanna and 201
seasonal ecosystems, indicating an increase in grasses as tree density is reduced. 202
In some scenarios, the woody dominant life form (either trees or shrubs) shifts to grasses (red 203
areas in Fig. 3d) but this trend is uncommon: it is likely in less than 2% of the area. No changes 204
from grasses to shrubs or trees are expected. 205
4. Discussion 206
The changes in the water cycle reflect changes in precipitation and temperature but also in 207
vegetation density and structure and, therefore, hydrological impacts result from diverse 208
equilibrium states between these climate components. 209
Under a general drying trend in climate scenarios (lower precipitation combined with higher 210
temperatures), we found that runoff, evapotranspiration and LAI have mixed (positive and 211
negative) spatial patterns of change. Similar to climate uncertainties, the higher the emissions the 212
lower the uncertainty (between models) of ecosystems and hydrologic responses. 213
In some areas runoff is likely to decrease even though precipitation change is uncertain. We 214
found likely runoff decreases and evapotranspiration increases in most of Panama and southern 215
Costa Rica where 30-60% of scenarios show an increase in precipitation and the complement the 216
opposite signal. The increased certainty of the impacts is due to the increase in temperature 217
(across all scenarios) that drives a non-linear increase in evapotranspiration at the expense of 218
runoff. 219
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
11
Runoff is likely to increase in areas where grass LAI increases and where evapotranspiration 220
decreases, mostly central Honduras, Guatemala, and mountains in Mexico. This trend is 221
observed in relatively dry areas, where current annual runoff and precipitation are less than 200 222
mm and 1000 mm respectively and probably results from the reduction in deep woody roots, 223
which extract deep water. 224
The increase in evapotranspiration in humid areas is driven by the increase in temperatures, 225
which compensates the effects of decreased LAI on reduced evapotranspiration. Therefore, in 226
these areas, the virtually likely increase in temperature results in a likely decrease in runoff, even 227
where the future trend in precipitation is uncertain. In drier areas, runoff can increase even 228
though the future climate appears to be drier because decreased water availability reduces 229
vegetation LAI, evapotranspiration, and woody roots and causes a larger fraction of precipitation 230
to run off (Aber et al. 2001). 231
Future changes in LAI and potential vegetation life forms imply modifications in the density 232
and structure of vegetation, ecosystems and their functions, particularly in areas where a shift 233
from tree to grass dominated vegetation types is expected. Mesoamerican ecosystems will shift 234
to drier types, particularly in areas where runoff and evapotranspiration are both reduced 235
indicating that precipitation falls below the potential evapotranspiration, and the water 236
availability for vegetation is reduced (i.e. central Yucatan). Increased evapotranspiration in other 237
areas (e.g. Costa Rica and Panama) indicate that under climate change the 238
runoff:evapotranspiration ratio decreases and a larger fraction of precipitation can still be used 239
by vegetation. 240
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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A global study by Scholze et al. 2006), using the Lund-Potsdam-Jena (LPJ) dynamic 241
vegetation model at a coarser resolution, found qualitatively similar trends for runoff and LAI 242
changes in Mesoamerica but with differences compared to our study; for example, larger areas of 243
forest loss and increased runoff in the southern part of the region as opposed to the likely 244
decreased runoff found in our study. Comparing the two studies is not straightforward because of 245
the vastly different spatial resolutions (ca. 50 km vs. 1 km) and they grouped the climate 246
scenarios differently (by range of temperature increase vs. by emission scenarios in our study). 247
Also, the different results may come from the different thresholds used to estimate changes (33% 248
of observed variability vs. 20% in our study). These different resolutions and thresholds may 249
explain the smaller number of changes in our study. Yet, it is encouraging (regarding 250
uncertainties) to see similarities in the vegetation shifts between the results of the high resolution 251
climate scenarios used in MAPSS and those of the more coarse resolution scenarios in the LPJ. 252
The MAPSS-modeled changes in tree fractional cover, which results in structural ecosystem 253
changes, call for in-depth future studies of populations, species, and community ecology. For 254
example, changes in the dominant form (from trees to grasses) imply changes in seed sizes 255
(Moles et al. 2007) and a modification of migration rate, a capacity that is important for forming 256
new species assemblages depending on where future new climates as well as current analogs will 257
be located in Mesoamerica (Neilson et al. 2005; Williams et al. 2007. Changes in vegetation will 258
also affect forest carbon stocks (Bunker et al. 2005). Since LAI can be used as a proxy for the 259
storage of carbon in soils and vegetation (Bachelet et al. 2001; Neilson 1993a), we can assume 260
that Mesoamerican ecosystems may be atmospheric carbon sources under future climate. Studies 261
with dynamic vegetation models at coarse spatial resolutions suggest that this trend will be 262
apparent in the second half of the century (Cramer et al. 2001). 263
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
13
Changes in vegetation have implications for biodiversity. Our results highlight the potential 264
vulnerability of ecosystems in dry areas and their importance as a source of genes and species 265
that could help ecosystems shifting to drier types, for example, the Mexican dry forests (Dick; 266
Wright 2005). This could mean that changes in the network of protected areas and biological 267
corridors of the Mesoamerican Biological Corridor (MBC) are needed, as it has been suggested 268
for Canada’s national park system (Scott et al. 2002). Changes in the water cycle will also have 269
implications for terrestrial biodiversity. Water availability has been used as a determinant of 270
plant species richness in warm areas (Hawkins et al. 2003), since climate and ecosystem 271
productivity influence species richness (Field et al. 2009; Kreft; Jetz 2007). For example, 272
evapotranspiration was found to be correlated with global richness of vascular plants (Kreft; Jetz 273
2007) as well as terrestrial vertebrates of the Neotropics (Qian 2010). 274
The interactions between gradual climate change and other drivers of changes in ecosystems 275
and the water cycle clearly need more research on: (i) feedbacks between vegetation change and 276
fires, as changes in fire regimes may affect ecosystems and the climate-induced conversion of 277
forests to grasslands can modify fire regimes (Lewis 2006) (MAPSS contains a simplified fire 278
algorithm); (ii) hurricane and extreme events, which can be modified by climate change and have 279
impacts on the structure of forests (i.e. stem density and tree height) (Gillespie et al. 2006); (iii) 280
intra- and inter-annual climate variability, as variability affects the distribution of vegetation 281
types in Mesoamerica (Lozano-García et al. 2007), which is specially enhanced in complex 282
topography (Neilson 1993b); (iv) human disturbances, as deforestation, degradation, and 283
fragmentation influence water cycles (Piao et al. 2007) and increase ecosystem vulnerability to 284
climate change; (v) effects of elevated CO2 on LAI and evapotranspiration (Gedney et al. 2006). 285
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
14
Finally, this regional assessment could provide input for studies on the impacts of future 286
availability of water (for drinking water, irrigation or hydro-energy) and biomass (for household 287
firewood energy or forestry sectors) at scales below country level (Arnell 2004; Döll 2002) to 288
support the development of adaptation strategies to climate change in Mesoamerica. 289
Acknowledgements 290
This work was funded by the MESOTERRA Project of the Mesoamerican Agro-environmental 291
Program at the Tropical Agricultural Research and Higher Education Center (CATIE) and the 292
TroFCCA project executed by CATIE and CIFOR and funded by the European Commission 293
(contract EuropeAid/ENV/2004-81719). We acknowledge the Program for Climate Model 294
Diagnosis and Intercomparison (PCDMI) and the WCRP’s Working Group on Coupled 295
Modelling (WGCM) for their roles in making available the WCRP CMIP3 multi-model dataset. 296
The creation of this dataset was supported by the Office of Science, U.S. Department of Energy. 297
We thank The Nature Conservancy California and Kirk Klausmeyer for downscaling and 298
converting the climate data to ArcGIS format and Marko Scholze for providing the code for the 299
maps legends. 300
Appendix 1 Changes in leaf area index (LAI) and runoff for a range of change thresholds. 301
Insert Figure 1. 302
REFERENCES 303
Aber, J., R. P. Neilson, S. McNulty, J. M. Lenihan, D. Bachelet, and R. J. Drapek, 2001: Forest Processes 304 and Global Environmental Change: Predicting the Effects of Individual and Multiple Stressors. 305 BioScience, 51, 735-751. 306 Aguilar, E., and Coauthors, 2005: Changes in precipitation and temperature extremes in Central America 307 and northern South America, 1961–2003. Journal of Geophysical Research, 110. 308 Arnell, N. W., 2004: Climate change and global water resources: SRES emissions and socio-economic 309 scenarios. Global Environmental Change, 14, 31-52. 310
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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Figure captions 432
Figure 1. Region of study: relief, areas with natural vegetation cover (for the year 2000;CCAD; 433
WB 2003), watershed boundaries, and country limits. This and subsequent maps are based on the 434
Mollweide projection. 435
Figure 2. Precipitation and temperature changes in Mesoamerica under low (B1), moderate 436
(A1B) and high (A2) emission scenarios for 2070-2099 (48, 52 and 36 scenarios for B1, A1B 437
and A2). The likelihood of precipitation change is estimated as the percentage of models 438
showing a decrease in precipitation (column a). Bi-variate color maps (b) combine projected 439
average precipitation and temperature changes across all scenarios. 440
Figure 3. Ratio of simulations in low (B1), moderate (A1B) and high (A2) emission scenarios 441
showing at least 20% change in runoff (a), 20% in evapotranspiration (b), 20% in leaf area index 442
(c) or change in dominant life form (d). The horizontal (vertical) axis of the color map is the 443
percentage of scenarios showing an increase (decrease) in runoff, evapotranspiration or LAI, or a 444
change from grass to shrub/tree (tree/shrub to grass). Legend values show mean range value for 445
each color class. 446
Figure 4. Ratio of simulations in low (B1), moderate (A1B) and high (A2) emission scenarios 447
showing a change of at least 20% change in the leaf area index of trees (a), shrubs (b) and 448
grasses (c). The horizontal (vertical) axis of the color map is the percentage of scenarios showing 449
an increase (decrease). Legend values show mean range values for each color class. 450
Figure captions– Appendix 1 451
452
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
19
Figure 1. Percentage of area under different likelihoods of change in runoff and leaf area index 453
(LAI) in Mesoamerica in 2070-2099, depending on the threshold above which changes are 454
observed. Low (B1) (left hand column a, b, c, d, e, and f) and high (A2) (right-hand column g, h, 455
i, j, k, and l) emissions scenarios are presented. Area for each likelihood category is presented for 456
decreases (a-g, c-i, and e-k) and increases (b-h, d-j, and f-l) in runoff, evapotranspiration and 457
LAI. 458
459
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
20
Figure 1 460
461
Figure 1. Region of study: relief, areas with natural vegetation cover (for the year 2000;CCAD; 462
WB 2003), watershed boundaries, and country limits. This and subsequent maps are based on the 463
Mollweide projection. 464
465
466
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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Figure 2 467
468
Figure 2. Precipitation and temperature changes in Mesoamerica under low (B1), moderate 469 (A1B) and high (A2) emission scenarios for 2070-2099 (48, 52 and 36 scenarios for B1, A1B 470 and A2). The likelihood of precipitation change is estimated as the percentage of models 471 showing a decrease in precipitation (column a). Bi-variate color maps (b) combine projected 472
average precipitation and temperature changes across all scenarios. 473
474
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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Figure 3 475
476
Figure 3. Ratio of simulations in low (B1), moderate (A1B) and high (A2) emission scenarios 477
showing at least 20% change in runoff (a), 20% in evapotranspiration (b), 20% in leaf area index 478 (c) or change in dominant life form (d). The horizontal (vertical) axis of the color map is the 479 percentage of scenarios showing an increase (decrease) in runoff, evapotranspiration or LAI, or a 480
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
23
change from grass to shrub/tree (tree/shrub to grass). Legend values show mean range value for 481
each color class. 482
483
484
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
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Figure 4 485
486
Figure 4. Ratio of simulations in low (B1), moderate (A1B) and high (A2) emission scenarios 487
showing a change of at least 20% change in the leaf area index of trees (a), shrubs (b) and 488 grasses (c). The horizontal (vertical) axis of the color map is the percentage of scenarios showing 489
an increase (decrease). Legend values show mean range values for each color class. 490
491
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
25
Appendix 1 492
0%
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10 20 30 40 50 60 70 80 90
Runoff decrease (%)
A2
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Runoff increase (%)
0%
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)
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B1
0%
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10 20 30 40 50 60 70 80 90
Evapotranspiration decrease (%)
0%
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a (%
)
Evapotranspiration decrease (%)
493
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
26
0%
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Virtualy likely very likely likely about as likely as not
unlikely very unlikely exceptionally unlikely
0%
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LAI increase (%)
0%
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LAI decrease (%)
0%
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LAI decrease (%)
0%
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Are
a (%
)
Evapotranspiration increase (%)
0%
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10 20 30 40 50 60 70 80 90
Evapotranspiration increase (%)
0%
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Are
a (%
)
LAI increase (%)
494
Imbach, P, Molina, L., Locatelli B., Roupsard O., Mahé G., Neilson R., Corrales L., Scholze M., Ciais P. (2012). Modeling potential equilibrium states of vegetation and terrestrial water cycle of Mesoamerica under climate change scenarios. Journal of Hydrometeorology, 13, 665-680.
27
Figure 1. Percentage of area under different likelihoods of change in runoff and leaf area index 495 (LAI) in Mesoamerica in 2070-2099, depending on the threshold above which changes are 496
observed. Low (B1) (left hand column a, b, c, d, e, and f) and high (A2) (right-hand column g, h, 497 i, j, k, and l) emissions scenarios are presented. Area for each likelihood category is presented for 498 decreases (a-g, c-i, and e-k) and increases (b-h, d-j, and f-l) in runoff, evapotranspiration and 499
LAI. 500