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A distributed parameter model Soil and Water Assessment Tool (SWAT) has been tested on daily and monthly basis for estimating surface runoff and sediment yield from a small watershed "Chhokeranala" in eastern India using satellite data and Geographical Information System (GIS). Several maps like watershed and sub-watershed boundaries, drainage network, landuse/cover and soil texture have been generated. The SWAT model has been verified for the initial phase of monsoon season in the year 2002 using daily rainfall and air temperature. Performance of the model has been also evaluated to simulate the surface runoff and sediment yield on subwatershed basis for two months (July-August 2002). The results show a good agreement between observed and simulated runoff and sediment yield during the study period. Capability of the model for generating rainfall has been evaluated for 10 years (1992 -2001) period. The model simulated daily rainfall shows close agreement with the observed rainfall. The present results show that the SWAT model can be used for satisfactory simulation of daily and monthly rainfall, runoff and sediment yield. In~oducfionEstimation of hydrological parameters including runoff and sediment yield of a watershed is prerequisite for developing the best management plan for sustainable crop production. Surface hydrologic modelling of watershed mainly includes processes like runoff and movement of sediment as well as pollutants from the watershed to the outlet. Estimation of runoff and sediment yield is necessary for the design of soil conservation structures and for identifying the critical erosion prone areas of a watershed for implementation of best management plan with limited resources.

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Global warming is casting its shadow in the form of climatic changes that is affecting the local weather conditions which has its bearing on crop production and water availability, the basic necessities for survival of life on the planet. In the present study, an attempt was made to investigate the cause of poor production of cotton in 2011-12 in Surat, Gujarat as compared to 2012-13 and 2013-14. Weather data since 2000 was analyzed and compared with the data of 2011-12 and comparison was made to find the abnormality in cotton crop productivity. It was found that during 2011-12, there was delayed monsoon, as well as during squaring and flowering stage (i.e. in August 2011) there was high rainfall (595.6 mm), maximum and minimum temperatures were above normal, during development (June-August) and flowering stage of crop (October-December) which disturbed the crop physiology indirectly affecting the yield of cotton. The combined effect of rainfall and temperature was on relative humidity that created conducive atmosphere for insect and pest attacks on crops. Due to changes in temperature and relative humidity, evaporative water demands would have further aggravated the watering needs of crop. The study concludes that erratic monsoon or delayed monsoon hampers crop physiology ultimately yield due to erratic weather conditions. Further, such changes in cotton growing areas could form the basis of planning and decisions on pricing, crop insurance, export and import policies of cotton crop.