ISPRS Archives XXXVIII-8/W3 Workshop Proceedings: Impact of Climate Change on Agriculture 366 LONG TERM TREND ANALYSIS OF SURFACE INSOLATION AND EVAPORATION OVER SELECTED CLIMATE TYPES IN INDIA

The atmospheric radiative forcing is a central theme of climate change impact studies. The presence of Atmospheric Brown Clouds due to increased aerosol concentrations and green house gases such as water vapour, CO2 alter solar radiation and atmospheric thermal regimes. Both have strong feedbacks on open water evaporation. The measured daily global (direct + diffuse) insolation for a period of more than fifty years (1960-2003) and diffuse insolation for the period of 30 yrs (1973-2003) were analyzed over four stations in India representing different climate types. Weekly pan evaporation of Lysimetric stations was analyzed for the period 1975-1994 to explain inter-relations of insolation and evaporation trends. The annual, pentad (five years’ average) and decadal (ten years’ average) insolation at all stations showed average solar dimming rate varying between 1.15 to 3.35 % per decade. During 1975 to 1994, a significant increase in annual diffuse insolation was observed at arid station, Jodhpur which could be due to increase in concentration of dust aerosols leading to atmospheric cooling. Both solar dimming and atmospheric cooling triggered a substantial reduction in pan evaporation. But in some stations such as New Delhi, pan evaporation did not decrease in spite of decrease in global radiation. This indicated least role of aerosol but trade-off between increase in air temperature and solar insolation cut by green house gases and clouds, respectively. The study emphasizes the strong need to have detailed investigation about the impact of air quality on surface physical (e.g. lake evaporation) and biophysical (e.g. evapotranspiration) processes at different microclimates of India. [email protected]