Examining the spatial characteristics of rainfall during drought periods in the

Caribbean using CHIRPS

José J. Hernández Ayala, Michael Heslar and Sabina Osman

Department of Geography University of Florida

Drought in The Greater Antilles of The Caribbean

Drought Definitions

• Droughts are commonly defined as meteorological, agricultural, or hydrological.

• Meteorological droughts are periods of below-normal rainfall.

• Agricultural droughts, follow meteorological droughts and affect crops as well as natural flora and fauna.

• A hydrological drought is manifested by reduced streamflow, and lowered groundwater and lake levels

Problem Statement• The Caribbean is expected to become dryer

by the end of the century.• More frequent droughts will bring more

environmental and socio-economic issues.

• This research focuses on two main questions:

Which of the recent droughts has been the one that has affected most of the region?

Were there spatial similarities in rainfall patterns during recent drought periods ?

Study Area

<VALUE>

LegendVALUE

-44 -

63

63.1

- 160

161 -

293

294 -

453

454 -

634

635 -

851

852 -

1,12

0

1,130

- 1,47

0

1,480

- 1,90

0

1,910

- 2,97

0

Elevation (m)

Mean Rainfall Rainy Season (mm)

Causes of Drought in the Caribbean

• El Niño Southern Oscillation (ENSO)

Less tropical cyclonesStronger westerly flow

• North Atlantic Oscillation (NAO)

Less frontal systems moving to the Caribbean.

CHIRPS Data

• Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) is a 30+ year quasi-global rainfall dataset.

• Spanning 50°S-50°N (and all longitudes), starting in 1981 to near-present.

• CHIRPS incorporates 0.05° resolution satellite imagery with in-situ station data (Funk et al., 2015).

• Good for trend analysis and seasonal drought monitoring.

• Four drought periods were considered in this study (1994, 1997, 2009 and 2015).

• This study used three monthly total rainfall anomalies for four month groups (MJJ, JJA, JAS and ASO).

Methods • After pre-processing the CHIRPS anomaly

data (00-15 mean) all periods were classified in different groups.

• Extreme (-300 mm or more) anomalies • Severe (-299 to -100) anomalies • Moderate (-99 to -50) anomalies

• Overlay Analysis was implemented to examine spatial characteristics between events.

Results: Reclassify (JAS)

1994 (JAS) 1997 (JAS)

2009 (JAS) 2015 (JAS)

JAS Extreme Area (sq.km) JAS Severe Area (sq.km) JAS Moderate Area (sq.km)1994 3212.602281 1994 81549.58542 1994 44341.297031997 163.675758 1997 29693.99814 1997 33191.28472009 323.198921 2009 124168.2882 2009 74193.680462015 13273.28709 2015 152690.0972 2015 38973.52606

Total Rainfall Anomalies (mm)Extreme (-300 or >)

Severe (-299 to -100)

Moderate (-99 to -50)

Results: Group Month Comparisons

9%

7%

84%

Extreme MJJ Area (%)

13%

26%

10%

51%

Severe MJJ Area (%)

15%

37%22%

26%

Moderate MJJ Area (%)

16%

0%

83%

Extreme JJA Area (%)

35%

7%

20%

38%

Severe JJA Area (%)

32%

8%

31%

29%

Moderate JJA Area (%)

21%

8%

32%

39%

Severe JAS Area (%)

19%

1%2%

78%

Extreme JAS Area (%)

23%

17%

39%

20%

Moderate JAS Area (%)

23%

1%

24%

53%

Extreme ASO Area (%)

13%

11%

42%

33%

Severe ASO Area (%)

22%

27%21%

30%

Moderate ASO Area (%)

Results: Spatial Characteristics Extreme JJA Severe JJA Moderate JJA

Years Area Years Area Years Area1994-1997 57.49803 1994-1997 17914.76208 1994-1997 3322.7091994-2009 0 1994-2009 28893.64118 1994-2009 19644.061994-2015 1095.864 1994-2015 75114.88966 1994-2015 20684.131997-2009 0 1997-2009 8293.971722 1997-2009 3708.2791997-2015 59.33224 1997-2015 18352.41578 1997-2015 1444.3042009-2015 0 2009-2015 34549.21964 2009-2015 11673.72

Extreme ASO Severe ASO Moderate ASOYears Area Years Area Years Area1994-1997 61.99355 1994-1997 16669.99921 1994-1997 5103.5271994-2009 982.988 1994-2009 43053.01093 1994-2009 9638.5151994-2015 1206.287 1994-2015 27464.73788 1994-2015 12536.81997-2009 0 1997-2009 34324.00953 1997-2009 4219.0571997-2015 24.83789 1997-2015 35890.58789 1997-2015 11121.322009-2015 1340.962 2009-2015 114618.6283 2009-2015 11897.85

1994-2015 (Jun-Jul-Aug)

2009-2015 (Aug-Sept-Oct)

Total Rainfall Anomalies (mm) Extreme

Severe

Moderate

Results: Spatial Characteristics (Area %)

27%

3%

7%

12%25%

25%

Moderate MJJ

10%0%

9%

0%

19%61%

Severe MJJ

20%

72%

8%

Extreme MJJ

4% 5%

69%

3%4%

14%

Extreme JAS8%

21%

22%8%

8%

34%

Severe JAS

11%

30%

21%

11%

3%

24%

Moderate JAS

Conclusions• The 2015 drought was the event with the largest areas exhibiting extreme and severe

rainfall anomalies. • The 1994 and 2015 droughts were similar in their spatial characteristics of rainfall

(extreme and severe anomalies) for the earlier season months May to July and June to August.

• The 2009 and 2015 droughts were similar in their spatial characteristics of rainfall for July to September and August to October.

• The 1997 drought did not exhibit large areas with extreme or severe rainfall anomalies in the Caribbean when compared to other periods even though there was a strong ENSO event.

Future Research

• Future work will examine the atmospheric conditions (moisture, pressure, wind) of each of the drought periods to identify similarities or differences between them.

• Future studies will also look at the role that tropical cyclones (their absence or higher frequency) play in drought events in the Caribbean.

• Several teleconnections such as ENSO, NAO and AMO will be examined in order to understand their combined effects on drought periods in the Caribbean.

Questions?