Quantifying Climatic Risk In The Semiarid Tropics: ICRISAT Experience uri icon


  • Troll defined semiarid environments in terms of the average pcriod each year whenrainfall (R) exceeded potential evaporation (PE). In the semiarid tropics (SAT), rainfallchanges rapidly at the beginning and end of the monsoon so that thc pcriod whcn K >PE is insensitive to thc arbitrary way PE is dcfincd or mcasurcd.Hargreaves and Robertson used somewhat more sophisticated mcthods to spccify thclength of the growing season in terms of thc pcriod when "dependable' precipitation (i.e.the amount exceeded in at least 75% of years) was more than PE/3. This critcrion wasused in early work at ICRISAT. Later, a watcr balance model (WATBAI.) wasintroduced to cstimatc the risk of crop failure following dry spclls at any time duringthe monsoon.SORGF was the first simulation met tested at ICRISAT, calibrated with a set ofregional data, and then used for risk analysis. Recently, a simplcr simulation modcl(RESCRP) was developed to predict cmp responses to wcathcr and soil water. In thispresentation, an even simpler version is described and uscd to estimate yicldprobabilities at hvo sites with contrasting rainfall regimes as a function of niaxin~un~available water or of light interception. Ihe analysis demonstrates thc interaction ofweather, soil and plant factors in determining production risks.Many environmental constraints endured by crops and by farmers in thc SAT arc notyet amenable to modelling so that attempts to modcl risk, even with thc most con~plcxsimulation models, arc somewhat unrealistic. Major problems not yct adcquatclyaddressed by modellers includc germination, seedling establishmcnt and root pcnctrationin difficult soils, pests and diseases, and damage caused by wind or vcry heavy rain.Achieving the right balance between productivity and risk lies at thc base of allagricultural development. The SAT is an ecologically fragile region where thc productionof food is particularly hazardous bccausc rainfall is erratic, soils arc impoverished, andfew fanners are able to control pests and discases cffectivcly or to apply optimalamounts of fertiliser. Because population is growing faster than food supplies in manyparts of the SAT, subsistence agriculture has extended into marginal land, damaging theenvironment and threatening thc long-term viability of economic and social devclopmcnt.In this review, we identify salient environmental fcatures of thc SA'T and considcrbriefly some of the ways in which ICRISAT scientists have bccn ablc to rcduccproduction risks. We then assess progress in climatic analysis and indicalc thc directionsin which we believe the modelling of crop production should bc cncouragcd to dcvclop

publication date

  • 1991

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