Scale-invariance in space-time rainfall: Extension to climate scales

Interpretation of the impact of climate change or climate variability on water resources management, requires information at scales much smaller than the current resolution of regional or global climate models. The small-scale variability of precipitation is (typically) resolved by nested models or statistical downscaling. The latter framework is attractive in ensemble prediction due to its computational efficiency. To that end, recent work by Perica and Foufoula-Georgiou (1996) and Venugopal and Foufoula-Georgiou (1999) demonstrated the presence of scale invariance in space-time rainfall which can, in turn, be used to obtain precipitation at small-scales from large-scales. The research done therein focused on scales in the range of 2 - 32 km in space and 10 - 100 min in time. The work presented here has 2 objectives: (i) show that the hypothesis of scale-invariance in spatial rainfall fields extends to larger scales (of the order of 150 km) using gauge-adjusted radar analyses ``large-scale'' fields at 15km resolution over the contiguous United States, (ii) test for the presence of scale-invariance in precipitation fields obtained using weather and climate models. These results will be used in downscaling precipitation at climate scales (from climate model output) to hydrologic scales. This will followed by a quantitative comparison of the downscaled and observed output at small (hydrologic) scales.