A Precipitation Forecast Score Based on Potential Impact

In traditional contingency tables， the hit and false alarm events are given equal weights when calculating the precipitation TS score.The weight of missed precipitation events with different amounts that satisfy the threshold conditions is also the same.At the same time， the frequency calculation method for hit events of different precipitation amounts within the threshold range is also the same.However， these methods lack precision in the verification of high-resolution grid precipitation forecasts.In fact， the impact of differences in observed precipitation values， even when predictions hit the threshold， may be completely different.Additionally， the impact of differences in the forecasting and observation of precipitation values in missed precipitation events may also vary greatly.The article proposes a precipitation impact forecast score based on the comprehensive consideration of precipitation hit rate， missed alarm ratio， and precipitation amount."Impact" is defined as the characterization of potential consequences that may result from forecast hits or misses on actual precipitation occurrences.For hit and missed events， impact factors are defined by taking the logarithm of observed precipitation and the logarithm of the difference between observed and forecasted precipitation.Based on this， equivalent impacts （AI and CI） of hit and missed events are accumulated at the spatiotemporal scale.The scoring solely considering the impact of CI is defined as a sub-item of the Impact Threat Scoring （ITS）.The precipitation scoring that takes into account the combined effects of AI and CI is defined as the ITS score.Analysis shows that ITS0 assigns dynamic weights based on the degree of difference in missed precipitation， allowing for a clear distinction of the impact level of missed events.On the other hand， ITS rewards the accurate prediction of heavy precipitation.The larger the hit precipitation values and the smaller the difference between the forecasted and observed values in missed events， the larger the ITS score.These factors result in a better ability to depict the potential consequences on actual precipitation.