Abstract In semi-arid areas, such as the Northeast Region of Brazil (NRB), droughts lead to reduction of reservoir volumes and to increase of nutrient concentrations. The goal was to evaluate the trophic state index (TSI) of semi-arid reservoirs due to interannual variations of precipitation and stored volume. The study included 65 reservoirs in 8 NRB-based watersheds for 2008–2017. From 2013, NRB faced a severe drought that induced a significant reservoir volume reduction. Although the trophic state was already high before the drought (mostly eutrophic and hypereutrophic), the TSI of 91% of the reservoirs increased in the dry period. However, differently from the other watersheds, in which 100% TSI increase was observed for all reservoirs, the groundwater-rich and the lowest-water demand watersheds presented TSI decreases in 30 and 50% of the reservoirs, respectively. Thus, the impact of droughts on these two watersheds was less pronounced, as a potential result of groundwater flow with low-phosphorus concentration into the reservoirs of the former watershed, and lower nutrient loads/higher stored reservoir volumes of the latter one. Simple empirical equations, which are capable to estimate the mean TSI based solely on precipitation and reservoir volume, showed to be potential tools for integrated water management.

中文翻译：

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作为水文气候变化函数的半干旱水库营养状态变化

摘要 在巴西东北地区（NRB）等半干旱地区，干旱导致水库容积减少，养分浓度增加。目标是评估由于降水和储存量的年际变化引起的半干旱水库的营养状态指数（TSI）。该研究包括 2008-2017 年 8 个 NRB 流域的 65 个水库。从 2013 年开始，NRB 面临严重干旱，导致水库容积显着减少。虽然干旱前营养状态已经很高（主要是富营养化和超富营养化），但91%的水库在干旱期TSI增加。然而，与其他流域不同，在其他流域中，所有水库都观察到 100% 的 TSI 增加，富地下水流域和最低需水流域的 TSI 分别在 30% 和 50% 的水库中下降。因此，干旱对这两个流域的影响不那么明显，这是因为地下水以低磷浓度流入前一个流域的水库，而后一个流域的养分负荷较低/蓄水量较高。简单的经验方程能够仅根据降水量和水库体积估计平均 TSI，表明是综合水资源管理的潜在工具。后者的养分负荷更低/储存量更高。简单的经验方程能够仅根据降水量和水库体积估计平均 TSI，表明是综合水资源管理的潜在工具。后者的养分负荷更低/储存量更高。简单的经验方程能够仅根据降水量和水库体积估计平均 TSI，表明是综合水资源管理的潜在工具。