The impact of remotely sensed dynamic land surface conditions on the simulation of drought in Australia.

Using the Weather Research and Forecasting Model, feedbacks between albedo, vegetation fraction, soil moisture and drought over south-east Australia are investigated using time varying MODIS derived vegetation fraction and albedo data to update the lower boundary condition. Vegetation fraction changes lag precipitation reduction by 6 to 8 months in non-arid regions. With the onset of the drought, a fast physical mechanism with monthly time scale is found to play positive role in the soil moisture-drought feedback, and a slow biological mechanism provides a negative feedback in the soil moisture - drought interaction on an annual time scale. That is, in the short term a reduction in soil moisture leads to a reduction in the convective potential and hence precipitation, further reducing the soil moisture. If low levels of soil moisture persist long enough reductions in vegetation cover and vigour will occur, this reduces the evapotranspiration and hence the rate of soil moisture reduction, slowing the fast physical feedback. These feedbacks are space and time dependent. Overall the land surface feedbacks cause drought conditions to occur earlier and to be more severe at the peak by ~10-15%.