Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil; Instituto de Estudos Avançados, Universidade de São Paulo, São Paulo, Brazil.
School of Geography, University of Leeds, Leeds, United Kingdom.
Sci Total Environ. 2020 Nov 15;743:140798. doi: 10.1016/j.scitotenv.2020.140798. Epub 2020 Jul 8.
The impacts of climate change on precipitation and the growing demand for water have increased the water risks worldwide. Water scarcity is one of the main challenges of the 21st century, and the assessment of water risks is only possible from spatially distributed records of historical climate and levels of water reservoirs. One potential method to assess water supply is the reconstruction of oxygen isotopes in rainfall. We here investigated the use of tree-ring stable isotopes in urban trees to assess spatial/temporal variation in precipitation and level of water reservoirs. We analyzed the intra-annual variation of δC and δO in the tree rings of Tipuana tipu trees from northern and southern Metropolitan Area of São Paulo (MASP), Brazil. While variation in δC indicates low leaf-level enrichments from evapotranspiration, δO variation clearly reflects precipitation extremes. Tree-ring δO was highest during the 2014 drought, associated with the lowest historical reservoir levels in the city. The δO values from the middle of the tree rings have a strong association with the mid-summer precipitation (r = -0.71), similar to the association between the volume of precipitation and its δO signature (r = -0.76). These consistent results allowed us to test the association between tree-ring δO and water-level of the main reservoirs that supply the MASP. We observed a strong association between intra-annual tree-ring δO and the water-level of reservoirs in the northern and southern MASP (r = -0.94, r = -0.90, respectively). These results point to the potential use of high-resolution tree-ring stable isotopes to put precipitation extremes, and water supply, in a historical perspective assisting public policies related to water risks and climate change. The ability to record precipitation extremes, and previously reported capacity to record air pollution, place Tipuana tipu in a prominent position as a reliable environmental monitor for urban locations.
气候变化对降水的影响以及对水资源需求的不断增长，使全球水资源面临的风险不断增加。水资源短缺是 21 世纪的主要挑战之一，而对水资源风险的评估只能基于历史气候和水库水位的空间分布记录。评估水资源供应的一种潜在方法是重建降雨中的氧同位素。我们在这里研究了利用城市树木的树木年轮稳定同位素来评估降水和水库水位的时空变化。我们分析了巴西圣保罗大都市区（MASP）北部和南部 Tipuana tipu 树木年轮中 δC 和 δO 的年内变化。虽然 δC 的变化表明从蒸腾作用中低叶片水平的富集，但 δO 的变化清楚地反映了降水极值。在 2014 年干旱期间，树木年轮 δO 最高，与城市历史最低水库水位相关。树木年轮中部的 δO 值与夏季中期降水呈强相关（r=-0.71），与降水与其 δO 特征之间的关系（r=-0.76）相似。这些一致的结果使我们能够检验树木年轮 δO 与供应 MASP 的主要水库水位之间的关联。我们观察到树木年轮 δO 与 MASP 北部和南部水库水位之间存在强烈关联（r=-0.94，r=-0.90）。这些结果表明，利用高分辨率树木年轮稳定同位素将降水极值和供水置于历史背景下，有助于制定与水资源风险和气候变化相关的公共政策。记录降水极值的能力，以及先前报道的记录空气污染的能力，使 Tipuana tipu 在作为城市环境监测的可靠工具方面处于突出地位。
