The Global Soil Moisture Data Bank

Soil moisture is an important variable in the climate system. Understanding and predicting variations of surface temperature, drought, and flood depen d critically on knowledge of soil moisture variations, as do impacts of cli mate change and weather forecasting. An observational dataset of actual in situ measurements is crucial for climatological analysis, for model develop ment and evaluation, and as ground truth for remote sensing. To that end, t he Global Soil Moisture Data Bank, a Web site (http://climate.envsci.rutger s.edu/soil_moisture) dedicated to collection, dissemination, and analysis o f soil moisture data from around the globe, is described. The data bank cur rently has soil moisture observations for over 600 stations from a large va riety of global climates, including the former Soviet Union, China, Mongoli a, India, and the United States. Most of the data are in situ gravimetric o bservations of soil moisture; all extend for at least 6 years and most for more than 15 years. Most of the stations have grass vegetation, and some ar e agricultural. The observations have been used to examine the temporal and spatial scales of soil moisture variations, to evaluate Atmospheric Model Intercomparison Project, Project for Intercomparison of Land-Surface Parame terization Schemes, and Global Soil Wetness Project simulations of soil moi sture, for remote sensing of soil moisture, for designing new soil moisture observational networks, and to examine soil moisture trends. For the top I -m soil layers, the temporal scale of soil moisture variation at all midlat itude sites is 1.5 to 2 months and the spatial scale is about 500 km. Land surface models, in general, do not capture the observed soil moisture varia tions when forced with either model-generated or observed meteorology. In c ontrast to predictions of summer desiccation with increasing temperatures, for the stations with the longest records summer soil moisture in the top 1 m has increased while temperatures have risen. The increasing trend in pre cipitation more than compensated for the enhanced evaporation.