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[1] A distributed biosphere hydrological model, the so-called water and energy budget-based distributed hydrological model (WEB-DHM), has been developed by fully coupling a biosphere scheme (SiB2) with a geomorphology-based hydrological model (GBHM). SiB2 describes the transfer of turbulent fluxes (energy, water, and carbon fluxes) between the atmosphere and land surface for each model grid. The GBHM redistributes water moisture laterally through simulating both surface and subsurface runoff using grid-hillslope discretization and then flow routing in the river network. The WEB-DHM was calibrated and validated for the Little Washita Basin using field observations from Southern Great Plains Hydrology Experiments (SGP97 and SGP99). For the SGP97 period, the model was calibrated and it shows an ability to reproduce point-scale energy fluxes (RMSE < 50 W m À2 ) as well as CO 2 flux (RMSE = 4.6 m mol m À2 s À1 ). At basin scale, the WEB-DHM can simulate a reasonable hydrograph (Nash = 0.956) and spatial soil moisture distribution with calibration of only a few soil hydraulic parameters for discharge. The model was then validated using SGP99 data sets and observed discharge. For the validation period, the model shows good performance in reproducing the soil surface temperature at 11 sites and the spatial distribution of surface soil moisture, as well as long-term discharges (Nash = 0.715) in the hydroyear from 1 September 1998 to 31 August 1999 that covers both the annual largest flood peak of 1999 and the SGP99 period. To our knowledge, this work is the first to undertake the development and evaluation of a distributed biosphere hydrological model using such comprehensive field observations.

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[1] Land surface hydrological modeling is sensitive to near-surface air temperature, which is especially true for the cryosphere. The lapse rate of near-surface air temperature is a critical parameter when interpolating air temperature from station data to gridded cells. To obtain spatially distributed, fine-resolution near-surface (2 m) air temperature in the mainland China, monthly air temperature from 553 Chinese national meteorological stations (with continuous data from 1962 to 2011) are divided into 24 regional groups to analyze spatiotemporal variations of lapse rate in relation to surface air temperature and relative humidity. The results are as follows: (1) Evaluation of estimated lapse rate shows that the estimates are reasonable and useful for temperature-related analyses and modeling studies. (2) Lapse rates generally have a banded spatial distribution from southeast to northwest, with relatively large values on the Tibetan Plateau and in northeast China. The greatest spatial variability is in winter with a range of 0.3°C-0.9°C · 100 m À1 , accompanied by an inversion phenomenon in the northern Xinjiang Province. In addition, the lapse rates show a clear seasonal cycle. (3) The lapse rates maintain a consistently positive correlation with temperature in all seasons, and these correlations are more prevalent in the north and east. The lapse rates exhibit a negative relationship with relative humidity in all seasons, especially in the east. (4) Substantial regional differences in temporal lapse rate trends over the study period are identified. Increasing lapse rates are more pronounced in northern China, and decreasing trends are found in southwest China, which are more notable in winter. An overall increase of air temperature and regional variation of relative humidity together influenced the change of lapse rate.

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Lake water storage change (DS w ) is an important indicator of the hydrologic cycle and greatly influences lake expansion/shrinkage over the Tibetan Plateau (TP). Accurate estimation of DS w will contribute to improved understanding of lake variations in the TP. Based on a water balance, this study explored the variations of DS w for the Lake Selin Co (the largest closed lake on the TP) during 2003-2012 using the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) together with two different evapotranspiration (ET) algorithms (the Penman-Monteith method and a simple sublimation estimation approach for water area in unfrozen and frozen period). The contributions of basin discharge and climate causes to the DS w are also quantitatively analyzed. The results showed that WEB-DHM could well reproduce daily discharge, the spatial pattern, and basin-averaged values of MODIS land surface temperature (LST) during nighttime and daytime. Compared with the ET reference values estimated from the basin-wide water balance, our ET estimates showed better performance than three global ET products in reproducing basinaveraged ET. The modeled ET at point scale matches well with short-term in situ daily measurements (RMSE 5 0.82 mm/d). Lake inflows and precipitation over the water area had stronger relationships with DS w in the warm season and monthly scale, whereas evaporation from the water area had remarkable effects on DS w in the cold season. The total contribution of the three factors to DS w was about 90%, and accounting for 49.5%, 22.1%, and 18.3%, respectively.

Energy budget-based distributed modeling of snow and glacier melt runoff is essential in a hydrologic model to accurately describe hydrologic processes in cold regions and high-altitude catchments. We developed herein an integrated modeling system with an energy budget-based multilayer scheme for clean glaciers, a single-layer scheme for debris-covered glaciers, and multilayer scheme for seasonal snow over glacier, soil, and forest within a distributed biosphere hydrological modeling framework. Model capability is demonstrated for Hunza River Basin (13,733 km 2 ) in the Karakoram region of Pakistan on a 500 m grid for 3 hydrologic years (2002)(2003)(2004). Discharge simulation results show good agreement with observations (Nash-Sutcliffe efficiency = 0.93). Flow composition analysis reveals that the runoff regime is strongly controlled by the snow and glacier melt runoff (50% snowmelt and 33% glacier melt). Pixel-by-pixel evaluation of the simulated spatial distribution of snow-covered area against Moderate Resolution Imaging Spectroradiometer-derived 8 day maximum snow cover extent data indicates that the areal extent of snow cover is reproduced well, with average accuracy 84% and average absolute bias 7%. The 3 year mean value of net mass balance (NMB) was estimated at +0.04 myr À1 . It is interesting that individual glaciers show similar characteristics of NMB over 3 years, suggesting that both topography and glacier hypsometry play key roles in glacier mass balance. This study provides a basis for potential application of such an integrated model to the entire Hindu-Kush-Karakoram-Himalaya region toward simulating snow and glacier hydrologic processes within a water and energy balance-based, distributed hydrological modeling framework.