Hydrologic forecasts verification and comparison of forecasting methods

Abstract

This paper presents the methods of estimating the mean square error of hydrological forecasts, allowing for assessment of their practical applicability. Depending upon the amount and composition of available hydrometeorological data, an appropriate method for forecast error estimation is chosen. A system of statistical tests for comparison of different forecasting methods for the same hydrologic characteristic with the same lead time is presented. These tests allow for choosing an optimal and most accurate forecasting method. Hydrological forecasting method efficiency estimation is based on comparing the forecast error with climatology or inertial (persistence) forecast error using presented tests. Keywords: hydrologic forecast verification, mean squared forecast error, methods of forecast error estimation, comparison of hydrologic forecasting methods, forecast applicability assessment. 1. Introduction The purpose of hydrologic forecasting is to predict the expected future water regime characteristics for rivers, channels, lakes, reservoirs, and other water bodies. Hydrologic forecasts are used for water resources management and water-related hazard management planning and operational activities. The quality of hydrologic forecasts is defined in turn by their accuracy and lead time. Therefore, the development of modern objective methods for evaluating the quality of operational river flow forecasting methods is of great scientific and practical importance [11, 12]. To estimate deterministic hydrologic forecast error and to assess the forecast applicability, the system of statistical methods is recommended. The use of those methods allows for obtaining objective quality assessment of hydrologic forecasting algorithms. Using these methods allows for selecting optimal scheme and developing scheme enhancement strategies taking into account the specific features of forecasting scheme, as well as the amount of hydrologic and meteorological data, their contents and quality investigated during scheme development, testing and operational use. Forecast verification implies statistical analysis of the relation between actual values of hydrologic regime elements and their forecast values using this scheme. Verification procedures are the final necessary step to complete the process of forecast scheme development and implementation. Hydrological forecast error determination and analysis are an essential step in the process of scheme development and operation. First of all, for a given forecast lead time, forecast error is the key index of practical value of that forecast. Moreover, forecast error analysis allows for determining scheme weaknesses and outlining strategies for scheme enhancement. Analysis results for a set of forecast of different elements of hydrologic regime within a whole region may determine and prove the strategies for improving the observation network and data acquisition and processing system. In case when different methods may be used for forecasting the same hydrologic characteristic with the same lead time, there is a need to choose the most accurate method. If an advanced modification