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

This study analyzes the results of monthly and seasonal precipitation forecasting from seven different global climate forecast models for major basins in Israel within October–April 1982–2010. The six National Multimodel Ensemble (NMME) models and the ECMWF seasonal model were used to calculate an International Multimodel Ensemble (IMME). The study presents the performance of both monthly and seasonal predictions of precipitation accumulated over three months, with respect to different lead times for the ensemble mean values, one per individual model. Additionally, we analyzed the performance of different combinations of models. We present verification of seasonal forecasting using real forecasts, focusing on a small domain characterized by complex terrain, high annual precipitation variability, and a sharp precipitation gradient from west to east as well as from south to north. The results in this study show that, in general, the monthly analysis does not provide very accurate results, even when using the IMME for one-month lead time. We found that the IMME outperformed any single model prediction. Our analysis indicates that the optimal combinations with the high correlation values contain at least three models. Moreover, prediction with larger number of models in the ensemble produces more robust predictions. The results obtained in this study highlight the advantages of using an ensemble of global models over single models for small domain

Assessment of the capacity for flood monitoring and early warning in Enlargement and Eastern/ Southern Neighbourhood countries of the European Union

Flooding is a natural disaster that can damage large areas in the vicinity of rivers, and in the case of flash floods, also in the vicinity of smaller streams. The Global Risks Report 2017 lists extreme weather events, of which flooding is the main risk in most countries, as the risk with the second highest potential impact and the highest likelihood of occurrence. It furthermore seems likely that climate change will aggravate flood impacts in many regions. This report presents an assessment of the capacity for flood monitoring and early flood warning in 17 of the 22 countries which belong to the Eastern and Southern neighbourhood policy of the European Union and the enlargement candidate countries. Many of these receive external funding to improve their systems, but this is often on an ad hoc basis and through individual projects.JRC.E.1-Disaster Risk Managemen

Comparing one-way and two-way coupled hydrometeorological forecasting systems for flood forecasting in the mediterranean region

A pair of hydro-meteorological modeling systems were calibrated and evaluated for the Ayalon basin in central Israel to assess the advantages and limitations of one-way versus two-way coupled modeling systems for flood prediction. The models used included the Hydrological Engineering Center-Hydrological Modeling System (HEC-HMS) model and the Weather Research and Forecasting (WRF) Hydro modeling system. The models were forced by observed, interpolated precipitation from rain-gauges within the basin, and with modeled precipitation from the WRF atmospheric model. Detailed calibration and evaluation was carried out for two major winter storms in January and December 2013. Then, both modeling systems were executed and evaluated in an operational mode for the full 2014/2015 rainy season. Outputs from these simulations were compared to observed measurements from the hydrometric station at the Ayalon basin outlet. Various statistical metrics were employed to quantify and analyze the results: correlation, Root Mean Square Error (RMSE) and the Nash–Sutcliffe (NS) efficiency coefficient. Foremost, the results presented in this study highlight the sensitivity of hydrological responses to different sources of simulated and observed precipitation data, and demonstrate improvement, although not significant, at the Hydrological response, like simulated hydrographs. With observed precipitation data both calibrated models closely simulated the observed hydrographs. The two-way coupled WRF/WRF-Hydro modeling system produced improved both the precipitation and hydrological simulations as compared to the one-way WRF simulations. Findings from this study, as well as previous studies, suggest that the use of two-way atmospheric-hydrological coupling has the potential to improve precipitation and, therefore, hydrological forecasts for early flood warning applications. However, more research needed in order to better understand the land-atmosphere coupling mechanisms driving hydrometeorological processes on a wider variety precipitation and terrestrial hydrologic systems

Climate change impacts on streamflow at the upper Jordan River based on an ensemble of regional climate models

Study Region: The upper Jordan River is the major water resource in Israel, a country which suffers from increasing shortage of natural water resources. Study Focus: In this study, we apply for the first time to this area an approach based on an ensemble of regional climate models, verify their trends vs. observations for a control period and use them for simulating future discharges of the Jordan River. New Hydrological Insights for the Region: The results of this study show that the observed negative trend of precipitation for the control period is also simulated by the climate models ensemble and projects a continued decreasing trend to the near future and further into the far future. Using the GR6J daily hydrological model for evaluating the effects of the predicted climate changes on the hydrological cycle in the region shows an increase in potential evaporation and a decrease in streamflow volumes in the Jordan River, Northern Israel. The results reveal and quantify the changes in rainfall–runoff relationships. These changes in the hydrological cycle in the region can be explained by changes in precipitation distribution and duration and decrease in soil moisture caused by the increase in evaporation. Results presented in this study could imply major consequences for the region. The findings here are relevant not only to Israel but also to the surrounding countries. Keywords: Rainfall - runoff relationships, Ensemble of regional climate models, Changes in the hydrological cycl

Physical/Statistical and Modeling Documentation of the Effects of Urban and Industrial Air Pollution in California on Precipitation and Stream Flows in Mountainous Terrain Downwind

This research achieved insights into the documented impacts of urban and industrial air pollution on orographic clouds and precipitation (and the resulting stream flows) over the California Sierra Nevada, downwind of the pollution sources. The pollution aerosols are submicron cloud condensation nuclei (CCN) that are incorporated into the orographic clouds, thereby slowing the coalescence of raindrops and riming on ice precipitation and delaying the conversion of cloud water into precipitation. The net rain‐volume losses in the polluted central and southern California Sierra Nevada are estimated at 4 x 109 cubic meters (m3) of water per year. This project’s accomplishments are threefold. First, it demonstrated through hydrological analyses that the negative effect of pollutants on mountain precipitation also results in stream flow losses. Second, quantitative analyses of cloud structure using multi‐spectral satellite imagery showed that the cloud precipitation‐forming processes are being suppressed in the same Sierra Nevada regions that are experiencing losses in precipitation and stream flows. Third, the results of numerical modeling simulations showed good agreement with precipitation and stream flow analyses based on observations that submicron CCN pollution can alter Sierra precipitation. This study’s finding that aerosols have been suppressing precipitation in high‐elevation areas in California for many years carries significant implications for the state’s water supply

Modeling the Effects of Land-Cover Change on Rainfall-Runoff Relationships in a Semiarid, Eastern Mediterranean Watershed

Temporal changes and spatial patterns are often studied by analyzing land-cover changes (LCCs) using spaceborne images. LCC is an important factor, affecting runoff within watersheds. The objective was to estimate the effects of 20 years of LCCs on rainfall-runoff relations in an extreme rainfall event. A 1989 Landsat TM-derived classification map was used as input for a Kinematic Runoff and Erosion (KINEROS) hydrological model along with the precipitation data of an extreme rainfall event. Model calibration was performed using measured runoff volume data. Validation of the model performance was conducted by comparing the model results to measured data. A similar procedure was used with a 2009 land-cover classification map as an input to the KINEROS model, along with similar precipitation data and calibration parameters, in order to understand the possible outcomes of a rainfall event of such a magnitude and duration after 20 years of LCCs. The results show an increase in runoff volume and peak discharge between the time periods as a result of LCCs. A strong relationship was detected between vegetation cover and the runoff volume. The LCCs with most pronounced effects on runoff volumes were related to urbanization and vegetation removal