Land Surface Processes Simulation Over Thar Desert in Northwest India

Abstract

Land surface processes in data scarce arid northwestern India and their influence on the regional climate including monsoon are now gaining enhanced scientific attention. In this work the seasonal variation of land surface parameters and surface-energy flux components over Lasiurus sindicus grassland system in Thar Desert, western India were simulated using the mesoscale WRF model. The data on surface fluxes from a micrometeorological station, and basic surface level weather data from the Central Arid Zone Research Institute’s experimental field station (260 59’ 41”N;71o29’”10E), Jaisalmer, were used for comparison. Simulations were made for typical fair weather days in three seasons [12–14 January (peak winter); 29–31 May (peak summer), 19–21 August (monsoon)] during 2012. Sensitivity experiments conducted using a 5-layer soil thermal diffusion (5TD) scheme and a comprehensive land surface physics scheme (Noah) revealed the 5TD scheme gives large biases in surface fluxes and other land surface parameters. Simulations show large variations in surface fluxes and meteorological parameters in different seasons with high friction velocities, sensible heat fluxes, deep boundary layers in summer and monsoon season as compared to winter. The shortwave radiation is underestimated during the monsoon season, and is overestimated in winter and summer. In general, the model simulated a cold bias in soil temperature in summer and monsoon season and a warm bias in winter; the simulated surface fluxes and air temperature followed these trends. These biases could be due to a negative bias in net radiation resulting from a high bias in downward shortwave radiation in various seasons. The Noah LSM simulated various parameters more realistically in all seasons than the 5TD soil scheme due to inclusion of explicit vegetation processes in the former. The differences in the simulated fluxes with the two LSMs are small in winter and large in summer. The deep mixed layers are distributed in the northeastern parts in summer, northern areas in southwest monsoon and in southwestern parts during winter seasons and associated with the land-cover and vegetation dynamics. Our results present a baseline simulation study in this data scarce arid region.