PA33B - 1820 A Historical Analysis of the Relationship Between Rice Production and PDSI Values in Sri Lanka
J. Jacobi & G. Hornberger Vanderbilt Institute for Energy and Environment (VIEE) Corresponding Author: J. Jacobi ([email protected]) Vanderbilt University, Nashville, Tennessee
I. INTRODUCTION III. RESEARCH QUESTION AND APPROACH VI. DISCUSSION In Sri Lanka, farmers in major rice produc on areas of the country are • How are rice produc on and PDSI values correlated in the Mahaweli river watershed? • Trincomalee District already struggling to produce enough rice, a staple food of the local • Calculate PDSI for major rice produc on districts in the watershed • Posi ve correla on between • Compare PDSI values to historic rice produc on data rice produc on and PDSI diet, and a severe wet or dry spell could be ruinous. Faced with a Dry changing climate and a growing demand for rice, it is important to be IV. METHODOLOGY • Located in the dry zone • 0% rain-fed able to an cipate how clima c changes will affect rice produc on. We conducted an analysis of historic temperature, precipita on, and Calculate PDSI • Furthest district from the Trincomalee rice produc on sta s cs in order to determine the effects of extreme • Temperature data was gathered from Kandy and Trincomalee. Values in between the sta ons were majority of tanks and interpolated using historical temperature averages. reservoirs wet and dry spells on rice produc on. Historical temperature and Matale precipita on data were used to calculate the Palmer Drought • Precipita on data were obtained from Sri Lankan Department of Meteorology • Dry condi ons (low PDSI) Severity Index (PDSI) for a number of sta ons distributed throughout • PDSI was calculated for each temperature sta on and those within or near the districts were average to have a more direct impact find the district average for each growing season Intermediate the Mahaweli River watershed (MRW). Significant correla ons due to suscep bility to Wet between PDSI and rice produc on were found in the Matale and Compare to historic rice data reduced irriga on flows
Trincomalee districts. • Produc on and yield (produc on/harvested area) sta s cs were plo ed against PDSI values for • each season in each district. PDSI values in upstream districts were also plo ed against produc on Matale District and yield sta s cs in downstream districts • Nega ve correla on between II. BACKGROUND rice yield and PDSI • Correla on coefficients and p values were calculated for each plot FIGURE 4: Climate zones of Sri • Located on border of Lanka intermediate and wet zones V. RESULTS Modified from h p://cecar.org/groups/csdsiacc/wiki/7fd8e/ • ~24% rain-fed No correla on between rice and PDSI was found in the Polonnaruwa and Kandy districts. In the • Already in a very wet part of the country Trincomalee district, significant correla on was found between detrended rice produc on and PDSI in • District receives enough rain to grow rice without irriga on in the Yala season. In the Matale district, significant correla on was found between detrended yield and most years PDSI for the Maha season. • We er condi ons than normal (high PDSI) may flood fields and Trincomalee Trincomalee - Yala R = 0.51 result in a lower yield 20 P = 0.02 4.00 Matale Trincomalee 3.00 10 Polonnaruwa 2.00 Total Harvested Area (ha) 19,684 13,116 1.00 Matale 0 % Rain-fed Area 24 0 0.00 PDSI -10 -1.00 -2.00 VII. CONCLUSIONS Kandy (Thousand mt) • -20 -3.00 Climate zone has a clear impact on rela onship between rice produc on and PDSI 1991 1996 2001 2006 Rice Produc on Detrended • Wet climate in Matale makes the district more suscep ble to Time PDSI Produc on Detrended wet condi ons while the opposite is true in Trincomalee FIGURE 2: Detrended rice produc on values for the Yala growing season in the Trincomalee district • Region specific nature of PDSI must be taken into account are plo ed against PDSI values for the Trincomalee district. There is a significant (p < 0.05) posi ve when analyzing results correla on between detrended rice produc on values and PDSI. FIGURE 1: Major rice producing districts in the MRW • Posi on in irriga on system also has an impact on rela onship Modified from h p://en.wikipedia.org/wiki/File:Sri_Lanka_relief_loca on_map.jpg Matale - Maha between rice produc on and PDSI 1000 R = -0.50 4.00 • Districts further away from reservoirs and tanks can be more • MRW is the major rice producing region of Sri Lanka P = 0.03 likely to experience disrup ons in supply of irrigated water • Two growing seasons 500 2.00 • Yala (May-August) • A modified PDSI is needed to further analyze correla on between • Maha (September-March) 0 0.00
PDSI rice produc on and PDSI • Three climate zones • Polonnaruwa, the major rice producing district in the MRW, is -500 -2.00 • Wet (Kandy, Matale) almost completely irrigated • Intermediate (Matale, Polonnaruwa) • A drought index that takes into account irrigated water supply • -1000 -4.00 Dry (Polonnaruwa, Trincomalee) Yield Detrended (kg/ha) will be developed to determine effects of PDSI on rice 1992 1997 2002 2007 • Irriga on schemes produc on • En rely irrigated (Polonnaruwa, Trincomalee) Time Yield Detrended PDSI • Mix of irrigated and rain-fed (Kandy, Matale) FIGURE 3: Detrended rice yield values for the Maha growing season in the Matale district are plo ed VIII. ACKNOWLDGEMENTS • Reservoirs and tanks are mostly upstream near Kandy and against PDSI values for the Matale district. There is a significant (p < 0.05) nega ve correla on This work was supported by VIEE and the Na onal Building Research Matale between detrended rice yield values and PDSI. Organiza on of Sri Lanka.