Identification of temporal changes in hydrological regimes of river basins is an important topic in contemporary hydrology because of the potential impacts of climate change on river flow regimes. For this purpose, long-term historical records of rainfall (P), runoff (Q) and other climatic factors were used to investigate hydrological variability and trends in the Tajan River Basin over the period 1969–1998. Actual evaporation (E), rainfall variability index (d), evaporation ratio (CE) and runoff ratio (CQ) were estimated from the available hydroclimatological records. Mann-Kendall trend analysis and non-parametric Sen's slope estimates were performed on the respective time series variables to detect monotonic trend direction and magnitude of change over time. Rainfall variability index showed that 1973 was the wettest year (δ = +2.039) while 1985 was the driest (δ = -1.584). Also, decades 69–78 and 89–98 were recognized as the wettest and driest decades respectively. The gradient of variation of climatological parameters showed that during the study period, all three parameters of rainfall, evaporation and runoff have decreased and the variations of rainfall and evaporation were significant at the 95% level. Investigation of hydrological changes due of dam construction (1999) showed that the amount and annual distribution of discharge were completely different pre and post-dam construction. Discharge decreased in high water months and increased in low water months to meet water supply demands, especially for agriculture. The relationship between temperature and rainfall trends is compared for three stations in Mazandaran Province (Gorgan, Babolsar and Ramsar) from 1956 to 2003 and nine other stations with different statistical periods of 19–36 years, relating trends to northern hemisphere and global trends. Decreases in temperature were accompanied by decreases in rainfall, and vice versa. These trends were not observed in northern hemisphere and world scales, where temperature increases are accompanied by decreases in rainfall. These variations of hydroclimatological parameters show undesirable water resources situations during the statistical periods if the trend continues severe water resource crises.

由于气候变化对河流流态的潜在影响，识别流域水文状况的时间变化是当代水文学的重要课题。为此，使用了长期降雨（P），径流（Q）和其他气候因素的历史记录来调查1969-1998年塔扬河流域的水文变异性和趋势。实际蒸发量（E），降雨变化指数（d），蒸发率（CE）和径流率（CQ）是根据可用的水文气候记录估算的。对各个时间序列变量执行了Mann-Kendall趋势分析和非参数Sen斜率估计，以检测单调趋势方向和随时间变化的幅度。降雨量变化指数表明，1973年是最湿的一年（δ= +2。039），而1985年最干旱（δ= -1.584）。同样，分别被认为是最潮湿和最干燥的几十年是69-78岁和89-98岁。气候参数变化的梯度表明，在研究期间，降雨，蒸发和径流这三个参数均下降，并且降雨和蒸发的变化在95％的水平上是显着的。大坝建设引起的水文变化调查（1999年）显示，大坝建设前后的流量和年排放量完全不同。为了满足供水需求（特别是对农业），高水月份的排放量减少，而低水月份的排放量增加。比较了Mazandaran省（Gorgan，Babolsar和Ramsar）（从1956年至2003年）以及其他9个站，其统计期为19-36年，其趋势与北半球和全球趋势相关。温度的降低伴随着降雨的减少，反之亦然。在北半球和世界范围内没有观察到这些趋势，那里的温度升高伴随着降雨的减少。如果趋势持续严重的水资源危机，则水文气候参数的这些变化表明在统计时期内水资源状况不理想。在北半球和世界范围内没有观察到这些趋势，那里的温度升高伴随着降雨的减少。如果趋势持续严重的水资源危机，则水文气候参数的这些变化表明在统计时期内水资源状况不理想。在北半球和世界范围内没有观察到这些趋势，那里的温度升高伴随着降雨的减少。如果趋势持续严重的水资源危机，则水文气候参数的这些变化表明在统计时期内水资源状况不理想。