The Annual Variation and Closure of the Water Cycle for the Asian Continent

Abstract

The goal of the present study is to elucidate and assess the observed closure and annual variations of the water cycles for the Asian continent and its constituent climatic regions. For this purpose, heavy reliance is placed on simulation as well as observational data. The difference between moisture convergence (MC) and runoff (R) is used as an inverse measure of the closure. Areal averages of MC ? R are compared between different areas to decide on its scale dependency and also between different climatic regions categorized by Köppen's climate classification to investigate their annual variations. Atmospheric Model Intercomparison Project (AMIP) II standard output data were used for simulation. The normal annual means of hydrological variables averaged over the Asian continent are similar between the AMIP II ensemble (MOD) data and the observational (OBS) counterparts, even though MOD and OBS do not exactly agree in terms of their respective regions of distinctive features. In the Asian continent, both OBS MC ? R and MOD MC ? R are small but in the case of OBS the smallness was due to cancellation of two large and opposite MC ? Rs for the dry and mesothermal climatic regions. An appraisal of the closure for each climatic regions has been attempted through comparison between MOD MC ? R and OBS MC ? R. Nevertheless the relatively poor closures in these two climatic regions surely pose a problem for the simulation community. The mean annual variations of MOD MC and MOD R, averaged for the Asian continent and its climatic regions, respectively, were analyzed for their uncertainty using the Taylor diagram. MOD R in the dry regions and MOD MC in the microthermal and polar regions are unreliable.