The trends in land surface heat fluxes over global monsoon domains and their responses to monsoon and precipitation

Abstract

The climatology, trends and leading modes of land surface latent heat flux (LHF) and sensible heat flux (SHF) as well as their responses to monsoon and precipitation in global land monsoon domains are presented. During the past three decades, LHF and SHF have generally undergone a rising and decreasing trend (that is, (LHF+, SHF−)), respectively, in Asian, North African, Austrian, and South American monsoon domains. Moreover, the increasing rate of LHF was higher than the decreasing rate of SHF, which causes a decreased trend in Bowen ratio. Two other dominant trend patterns, (LHF−, SHF−) and (LHF+, SHF+), are observed in South African and South American monsoon domains, respectively. The trends in LHF and SHF are closely linked to increasing global monsoon intensity and precipitation, especially for the monsoon domain that has annual precipitation lower than 1300 mm yr−1. Singular value decomposition (SVD) analyses show that monsoon strength explains 25.2% and 22.2% total covariance of LHF and SHF respectively in the first modes, and that precipitation slightly raises the percentages up to 27.8% and 24% respectively. The increasing monsoon and precipitation on one hand favor more land surface available energy being converted into LHF; on the other hand they enhance the LHF by increasing the land surface net radiation. Moreover, remarkable phase shifts in LHF and SHF are observed for monsoon domains during late-1990s, which are in phase with those of precipitation and monsoon strength. The intensifying LHF and precipitation indicate the acceleration of hydrological cycle in global terrestrial monsoon domains.