Surface energy balance and its closure in arid grassland ecosystems: A case study over Thar desert

Abstract

A complete annual cycle of micrometeorological measurements were carried out to characterize the dynamics of radiation and energy balance over a grassland ecosystem at Central Arid Zone Research Institute experimental area at Chandan, Jaisalmer, India from INSAT-linked ISRO-AMS (Agro-Met Station). The daytime average dekadal latent flux for actual evapotranspiration (AET) showed substantially lower magnitude (15-115 Wm-2) (AET: 0.3 mmd-1 to 2.5 mmd-1) with prominent peak coincident to south-west monsoon and peak growth stage. Sensible heat fluxes showed a large variation from 54 to 340 Wm-2 with peak during summer and minimum during winter and monsoon seasons. More than 70% energy balance closure (EBC) was observed. The non-closure of energy balance periods were characterized by strong local advections in summer. The daytime average net radiation showed bimodal behavior (195 to 420 Wm-2) with primary peak in spring-summer and secondary peak coincident to the start of the withdrawal of south-west monsoon. Significant complementary exponential relation (Y=0.045 e12.13X, R2 = 0.65) was found between dekadal albedo and Bowen ratio which was generally high (1.5 to 5.3) with intermittent dips (0.3 to 1.3) coincident to wet spells. Similarly, the dekadal albedo showed a higher magnitude (0.15 to 0.39), recording the highest (0.39) in the month of April and the lowest (0.15) in the month of September post-monsoon period when green grass growth was maximum.