Evaluation of a distributed monthly water balance model to ‎determine catchment runoff in arid region using RS and GIS ‎‎(A case study in Yazd-Ardakan basin)‎

Fresh water is becoming a scarce resource of the arid region. The only option left to ýmanage with this situation is to conserve water resources. Since the amount of rainfall and ýevapotranspiration rate vary within a watershed, available water for surface and ýgroundwater recharge also varies both on spatial and temporal scales. Moreover, ýgroundwater recharge (and ultimately the total water yield) is directly influenced by the ýsoil texture and land cover in the watershed.ý
In this study, the distributed Thornthwaite-Mather water balance model for the Yazd-ýArdakan catchment in Iran was developed based on monthly precipitation, potential ýevapotranspiration maps and water holding capacity map. The amount of annual runoff ýfrom the catchment predicted by the model is 66.7 mmþ,þý which is accumulated in the plain ýand then salt desert. Half of discharge is contributed by the direct runoff and the ýgroundwater contribution is significant.ý
A statistical comparison of the estimated and the measured stream flow of Pishkouh show ýthe mean monthly and mean annual estimated and measured stream flows, the correlation ýcoefficient between measured and estimated stream flows, the mean monthly and annual ýpercentage error of estimation and the 90% confidence interval for the mean stream flow. ýSince the study of water balance using the TM method with the help of remote sensing ýand GIS was found to be very helpful in determining the amount of monthly runoff in an ýarid region like the Yazd-Ardakan catchment.ý