دانلود رایگان مقاله پیش بینی احتمالاتی تبخیر و تعرق مرجع با سیستم پیش بینی منطقه محدود

abstract

The increasing availability of operational limited area ensemble prediction systems (LEPS) opens up new opportunities for the application of weather forecasts in agriculture and water resource management. This study aims to evaluate the performances of probabilistic daily reference crop evapotranspiration (ET0) forecasts with lead times up to 5 days and a spatial resolution of 7 km, computed by using COSMO-LEPS outputs (provided by the European Consortium for small–scale modelling, COSMO), in a region of southern Italy known for its complex topography in proximity to the Mediterranean coastline. ET0 was estimated by means of three different estimation methods, i.e. the Hargreaves-Samani (HS), Priestley-Taylor (PT) and FAO Penman-Monteith (PM) equations, in order to assess the size of the weather forecast errors with models of different accuracies. Forecasts were verified with ground-based data from 18 automatic weather stations, and for two irrigation seasons. Performances were assessed with both deterministic indices, including BIAS, RMSE, correlation coefficients and coefficients of variation of the 16-member ensemble forecasts, and probabilistic metrics, such as the Brier skill score, reliability diagrams and relative operating characteristic. ET0 forecasts with PM equation were robust and reliable, with slight sensitivity to the forecast lead time. High performances were also achieved with HS and PT equations, except for locations close to the coastline, where large systematic errors affect the numerical weather forecasts.

5. Conclusions A more rational and efficient use of water in agriculture can be achieved by supplying accurate forecasts of reference evapotranspiration (ET0), which is one of the key factors for the assessment of crop water requirements and irrigation needs. A probabilistic approach is recognized as the most appropriate to cope with the uncertainty of weather variability in the short-medium term. Although statistical downscaling techniques of global ensemble forecasts have been proved to provide reliable forecasts (e.g. Tian and Martinez, 2014), their applicability is hindered by the need of large data sets of ground-based observations for their calibration. The operational availability of weather forecasts by limited area ensemble prediction systems (LEPS) offers new opportunities for developing reliable advisory services for agricultural management, particularly for rural areas where complete ground-based weather data are rare. To our knowledge, this is the first study to verify the ability of LEPS outputs to forecast reference evapotranspiration in the shortmedium range. COSMO-LEPS forecasts with a spatial resolution of 7 km and lead times up to five days were employed for forecasting daily ET0 in southern Italy, in a region where weather forecasting is quite challenging given its complex topography in proximity to the Mediterranean coastline. The numerical weather outputs were applied without any preliminary post-processing aimed at removing local systematic errors. Forecast performances were assessed with three different empirical methods for estimating ET0, in order to evaluate the size of the weather forecast errors with models of different accuracies.