Hydrologic and carbon services in the Western Ghats: Response of forests and agro-ecosystems to extreme rainfall events

天然森林生态系统的性质和功能调节着降雨如何被分配为地表径流、地下径流、地下水和蒸散，以及河流中沉积物的输出。它们还决定了这些生态系统中碳的固定、储存和流失的方式和数量。一般来说，森林在其生物量中储存的碳越多，释放到溪流中的水就越少。然而，对于长期和密集的人类使用的热带混合景观，以及几十年来退化的地点重新植树造林，情况并不一定如此。对于热带森林生态系统来说，关于这两种不同类型的功能如何联系在一起的信息很少，特别是在这些生态系统因人类使用而退化的情况下。我们更不知道生态系统的水文和碳功能如何应对极端降雨事件(每小时大量降雨)和高强度降雨。这种情况发生的频率更高，而且在西高止山脉和邻近的德干高原未来的气候变化下可能会增加，这支持了1.6亿人的生计和需求。此外，这种极端降雨事件对热带地区农业生态系统的影响也在很大程度上没有得到研究，特别是与作物破坏和土壤流失有关的影响。我们知识的空白之一是这样的极端暴雨是如何在空间和时间上分布的，以及这种降雨事件的空间分布如何与大片景观中不同的土地利用和土地覆盖相互作用，从而影响水文和碳动态。印度是全球植树造林的领先者之一，包括对自然物种的试验，在过去几十年里，为了各种好处，大片退化的土地得到了恢复或重新造林。目前，印度正在计划重新造林1000多万公顷，作为国家计划(绿色印度使命)的一部分，以封存碳并帮助调节全球大气二氧化碳。这些举措可以改变大面积的水和碳收支，并影响下游农业用水的可获得性。拟议的项目将使用现有数据，并在三年内产生新的数据，以帮助回答其中一些问题，填补我们知识的空白。这将有助于政策制定者了解极端降雨事件的性质以及森林退化和重新造林对水文和碳调节的影响。它还将能够评估不同生态系统(天然林、退化森林、重新造林地点和农业生态系统)在未来高强度或极端降雨事件条件下履行这些功能的能力。它还将帮助农业规划者确定极端降雨条件下农业土地利用的可持续性。绿色印度任务的执行将受益于关于最佳恢复目标地点和植被类型的信息。该项目还将产生重大惠益，满足全球对热带再造林最优战略的需求，印度正在带头采取这一战略。它将有助于指导根据各国分水岭发展方案选择恢复的分水岭，并有助于制定有助于保护自然生境和确保保护生态系统产品和服务的政策。

Overall summaryProperties and functions of natural forest ecosystems regulate how rainfall is partitioned into surface flow, sub-surface flow, ground-water and evapotranspiration and also the export of sediment in streams. They also determine how and how much carbon is fixed, stored and lost from these ecosystems. In general, the more carbon that a forest stores in its biomass, the less water that the forest releases into the stream. However, this is not necessarily true under tropical mixed landscapes subject to long-term and intense human use and also as degraded sites are reforested over decades. Information on how these two different types of functions are linked is sparse for tropical forest ecosystems, especially when these ecosystems are degraded by human-use. We know even less about how hydrologic and carbon functions of ecosystems respond to extreme rain events (lots of rain per hour) and high intensity rain. This is occurring with greater frequency and is likely to increase under future climate change in the Western Ghats and adjacent Deccan Plateau which supports livelihoods and needs of 160 Million people. Furthermore, the effects of such extreme rain events on agro-ecosystems in tropical landscapes are also largely unstudied, especially in relation to crop damage and soil loss. One of the gaps in our knowledge is how such extreme rain storms are distributed over space and time, and how this spatial distribution of rain events interacts with different land-use and land-cover in large landscapes to influence hydrology and carbon dynamics. India is one of the global leaders in forestation including experimenting with natural species and large areas of degraded land has been restored or reforested over the past several decades for various benefits. Currently India is planning to reforest over 10 Million Hectares as part of a national plan (Green India Mission) to sequester carbon and help regulate global atmospheric CO2. These initiatives can transform the water and carbon budgets over large areas and also influence availability of water for agricultural use downstream. The proposed project will use existing data and generate new data over three years to help answer some of these questions and fill gaps in our knowledge. This will help policy and decision makers understand the nature of extreme rainfall events and hydrologic and carbon regulatory effects of forest degradation and reforestation. It will also enable assessment of the ability of different ecosystems (natural forests, degraded forests, reforested sites and agro-ecosystems) to perform these functions under future conditions of high intensity or extreme rain events. It will also help agricultural planners determine the sustainability of agricultural land-use under conditions of extreme rain. The implementation of the Green India Mission will benefit from information on the best possible sites to target for restoration and with what type of vegetation. This project will also generate major benefits to the global need for the most optimal strategies in tropical reforestation in which India is taking the lead. It will help guide the selection of watersheds for restoration under the countries watershed development programmes and contribute to policies that help conserve natural habitats and ensure the conservation of ecosystem goods and services.