Climatological thresholds of daily rainfall

This technical note summarizes the results from daily rainfall data analysi s with relation to annual rainfall amounts. By investigating the behavior o f correlation coefficients between the annual rainfall amounts and the with in-the-year cumulative frequency distribution functions of wet days with va rious threshold rainfall depths, it was found that (1) the annual rainfall amount is weakly correlated with the number of either dry or wet days-thus, the zero rainfall depth is not a proper threshold for the explanation of d ry or wet years; and (2) there exist certain thresholds of daily rainfall d epth (the climatological thresholds) with which the cumulative frequency of wet days can be well related with the annual rainfall amount. Also with th is threshold, the wet and dry years can be seen divided clearly into separa te groups of the cumulative frequency distribution functions, without any o verlaps, which were common when using the zero rainfall depth as a threshol d. Because it is found that there exist certain thresholds to be used for e xplaining the annual rainfall amount changes, these might also be used effe ctively for the analysis of possible changes in flood or drought patterns c aused by global warming.