Statistical downscaling of seasonal precipitation in Israel

Abstract

Careful planning of the use of water resources is critical in the semi-arid eastern Mediterranean region. The relevant areas are characterized by complex terrain and coastlines, and exhibit large spatial variability in seasonal precipitation. Global seasonal forecasts provide only partial information of the precipitation as a result of their coarse spatial resolution. We present two statistical downscaling methods of global forecasts, both identifying past-analogue synoptic-weather patterns and their connection to precipitation at specific stations. The first method utilizes a classification of the large-scale weather patterns into regimes, and the other identifies the closest past analogues directly without grouping the weather events. The validation of the algorithms using NCEP/NCAR reanalyses and past precipitation observations at 18 stations shows that both methods provide good skill in predicting mean precipitation amounts and quantiles of the precipitation distribution, and in reproducing the observed inter-annual and spatial variability. Both methods show good correlations between predicted and observed precipitation amounts (∼0.8), and the downscaled precipitation reproduces the observed differences between the stations, which are not available in the coarse global models. Based on these results, we downscaled the operational global-seasonal forecasts issued by the NCEP CFS1.0 ensemble. This approach could also have utility in climate change scenario downscaling.

The Advantage of Using International Multimodel Ensemble for Seasonal Precipitation Forecast over Israel

“…As described in the previous section, seven rain gauges were chosen to represent the rainfall amounts in those basins. These rain gauges were also used for the seasonal analysis by Wu et al [7] and Rostkier-Edelstein et al [8]. Tables 2 and 3 and Figures 2(a)-2(f) present the correlation, RMSE, and NSE for the observed monthly precipitation at the northern (Table 2) and central (Table 3) forecast points versus each single model and the IMME model for lead one to five months' hindcast.…”

“…Previous studies have applied statistical downscaling methods for seasonal forecasting in the Middle East ( [7,8]). The analysis, however, was based only on the Climate Forecast System (CFS) model reanalysis data and not on real reforecasts, so they did not examine the skill of the seasonal forecasts for the various meteorological variables and for different lead times.…”

The Use of an Orographic Precipitation Model to Assess the Precipitation Spatial Distribution in Lake Kinneret Watershed

“…The skill of the CFS in predicting precipitation in the Eastern Mediterranean was assessed by [66,67] for the development of statistical downscaling procedure. Both studies however, relied on the coarse 2.5 • NCEP/NOAA reanalysis for identifying the rainfall predictors and carried those relationships in order to statistically downscale the CFS (version 1).…”

“…It is shown that rain events occurred within a narrow wind-direction band, with the largest events occurring for south-southwest wind and, during most of the large rainfall events (>65 mm·day −1 ), with the observed moisture flux being greater than 55 (gr/kg·m/s). The skill of the CFS in predicting precipitation in the Eastern Mediterranean was assessed by [66,67] for the development of statistical downscaling procedure. Both studies however, relied on the coarse 2.5° NCEP/NOAA reanalysis for identifying the rainfall predictors and carried those relationships in order to statistically downscale the CFS (version 1).…”

Weather regimes and analogues downscaling of seasonal precipitation for the 21st century: A case study over Israel

“…Rostkier‐Edelstein et al () developed a statistical downscaling methodology for seasonal precipitation in Israel based on this semiobjective synoptic classification. They have also proposed a direct use of selected analogues, as originally proposed by Lorenz ().…”