Influence of Land Cover Change on Regional Water Cycles in Eastern Siberia

This study evaluated the effect of recent eastern Siberian land surface changes, such as water surface expansion, on water-energy fluxes and precipitation and focused on land surface parameters using a threedimensional atmospheric model [the Japan Meteorological Agency Nonhydrostatic model (JMA-NHM)]. Five parameters were set (viz., surface albedo, evaporative efficiency, roughness length, heat capacity, and thermal conductivity), and a response of evaporation and precipitation was evaluated. Increased precipitation corresponded to 75% of the increased evaporation on interparameter average, indicating strong land-atmosphere coupling. Water-energy flux and precipitation responses to water surface expansion were evaluated by two methods: JMA-NHM and the parameter sensitivity method. The latter method used a linear combination of parameter sensitivity on the fluxes and precipitation and parameter changes with land surface change. JMA-NHM demonstrated an increase in evaporation and precipitation and a decrease in downward shortwave radiation with low-level cloud increases. The parameter sensitivity method gave the same order as JMA-NHM in the estimation. This method has minimal calculation cost; thus, water-energy flux and precipitation response with further water surface expansion and decreases in forest area were simulated, producing various land surface data. The enhancement of the precipitation response to evaporation was weak for further water surface expansion in the largely expandedwater surface area; however, the ratio increased dramatically for the small water surface expanding area, indicating intense water cycle enhancement at the beginning of water surface expansion. Although grassland formation from forest has minimal impact, if incoming downward shortwave radiation were to increase because of the disappearance of the forest shading effect and the water surface formed by permafrost melting, the water cycle would be enhanced intensely.