Watersheds of the Sky
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Watersheds of the Sky - the terrestrial origins of precipitation and the importance of landscapes for maintaining social-ecological resilience
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Watersheds of the Sky
- 1. Watersheds of the Sky the terrestrial origins of precipitation and the importance of landscapes for maintaining social-ecological resilience May 23, 2012 Patrick W. Keys Stockholm Resilience Centre and Keys Consulting Inc.
- 2. Moisture Recycling • Evaporation traveling through the atmosphere and falling out as precipitation e.g. Budkyo 1974; Lettau et al., 1979; Koster et al. 1986; Brubaker et al. 1993; Eltahir and Bras 1994; Savenije 1995 • Large regions of the terrestrial land surface provide evaporation for downwind precipitation e.g. Numaguti, 1999; Bosilovich and Chern, 2006; Dirmeyer and Brubaker, 2007; Dominguez and Kumar, 2008; Dirmeyer et al., 2009; van der Ent et al., 2010; Ellison et al., 2011; Keys et al., 2012 Atmospheric Atmospheric transport transport Evaporation Precipitation Evaporation Ocean Terrestrial land surface
- 3. Water Accounting Model (WAM) van der Ent et al. 2010
- 4. Backtracking precipitation • Reversing the WAM allows for the identification of specific evaporation source areas • The precipitationshed “…the upwind atmosphere and surface that contributes evaporation to a specific location’s precipitation.” Keys et al. 2010 • The precipitationshed is a first step towards managing upwind rainfall
- 5. Terrestrial evaporation dependent water-constrained, rainfed-agriculture
- 17. Interpreting results • Analysis reveals that many areas are dependent on recycled moisture and are vulnerable to changes in upwind moisture recycling. • These areas would benefit from a stable provision of moisture during the growing season • Upwind land-use planning should consider the benefits of maintaining the existing or integrating new tree cover into the agricultural landscape
- 18. Policy considerations • The precipitationshed is a spatially explicit method allowing the identification of stakeholders in source-sink relationships • Scientists working with land use change and ecology need to work more closely with hydrologists and climatologists (and vice versa) to move this science forward • Managers of different resource areas will need to cooperate on exchanging information and coordinate activities. • Need to understand which areas contribute the most evaporation, and whether we can expect sudden or surprising land-use changes.
- 19. Continuing questions • What other livelihoods are particularly vulnerable to changes in upwind evaporation? • How does agroforestry compare to ‘pure’ agriculture or ‘pure’ forest in terms of evaporation? • What existing institutions might serve as useful models for developing precipitationshed management institutions?
- 20. Thank you!
- 21. Precipitationshed W. Sahel (absolute)
- 22. E. China precipitationshed (absolute)
- 23. N. China precipitationshed (absolute)
- 24. E. Sahel precipitationshed (absolute)
- 26. Pakistan-India precipitationshed (absolute)
- 27. S. Africa precipitationshed (absolute)
Notas del editor
- In conjunction with:Ruud van der Ent, TU DelftLine Gordon, Stockholm Resilience CentreHolger Hoff, SEI-Stockholm & Potsdam InstituteRevekkaNikoli, TU DelftHubert Savenije, TU DelftOVERVIEWMoisture recyclingWAMPrecipitationshed conceptKeys et al. 2010 (Backtracking, WCRA, terrestrial dependence, Psheds, Vulnerability assessment, preliminary landscape analysis)Precipitationshed policy Big questionsLEAD IN TO NEXT SLIDE: “Lets start with a quick overview of moisture recycling…”
- LEAD IN TO NEXT SLIDE: Van der Ent et al. performed an analysis examining moisture recycling, specifically examining (among other things) the importance of continental evaporation to downwind, continental precipitation.
- Not all regions are equally dependent.MethodsDataset: ERA-Interim reanalysis datasetSpatial resolution: global 1.5 x 1.5 degreeTemporal resolution: 1999-2008, 6 hourlyOutput of analysis: 1. Total Precipitation, 2. Precipitation of Terrestrial Origin, and 3. Recycling RatioLEAD IN TO NEXT SLIDE: This paper sparked the idea that if moisture can be tracked forward in time, in a spatially explicit manner, then backtracking it would mean we could identify the specific upwind terrestrial regions that contribute to downwind precipitation…
- From van der Ent et al. my research team and I wanted to explore whether we could reverse the WAM to identify the source of rainfall for a specific location.To name this concept we use the term PRECIPITATIONSHED, defined as “…the upwind atmosphere and surface that contributes evaporation to a specific location’s precipitation.” The importance of this concept is rooted in the fact that it provides the conceptual and empirical framework for defining the spatial boundary for management of upwind evaporated moisture falling downwind.LEAD IN TO NEXT SLIDE: As a pilot test of this idea, we decided to identify the precipitationsheds for regions that are particularly dependent on upwind rainfall. We selected regions that were dominated by rainfed agriculture for their livelihoods and where we can expect small changes in precipitation to have large impacts on livelihoods.
- Summarize the figure.MethodsTo identify these areas we used Arid and semi-arid regions from a global hydroclimates dataset (FAO 2006)Rainfed agriculture from Portmann et al. (2010) – focusing on maize, millet and sorghum; because they are dryland crops; wheat was omitted because its growing season often was opposite of M,M, and STerrestrial evaporation dependence was defined as a location re-ceived more than 50% of its growing season rainfall from upwind terrestrial evaporationLEAD IN TO NEXT SLIDE: The backtracking analysis described earlier was performed for each of these sink regions for their individual growing seasons, and their precipitationsheds were mapped.
- This is the results table of the precipitationsheds analysis. It shows the size of the sink region Sink region growing seasonNations within the precipitationshedThe growing season rainfallFraction of rainfall received during the growing season as a percent of total annual precipitationRainfall originating from terrestrial origins LEAD IN TO NEXT SLIDE: To better understand this, we’ll zoom into the West Sahel sink region
- The W. Sahel is the largest sink region among the seven sink regions, and it receives 93% of annual rainfall during the growing season months (June through Oct). 64% of the rainfall during the growing season is of terrestrial origin.LEAD IN TO NEXT SLIDE: To better understand these numbers, lets look at the precipitationshed
- This version is the RELATIVE pshed, which represents the fraction of moisture in each grid cell that is transported to the sink region. In other words, this pshed represents the areas that contribute the most moisture per unit area, and also represent the area that is of importance for evaluating any land-cover changes since these regions potentially transport the most to the sink region. So, for example, if the Sudd Wetlands were drained in South Sudan and Sudan, then a large source of consistent evaporative moisture would be lost having potentially large impacts downwind.The shape of this pshed is interesting, since it suggests that changes in land-cover throughout the Sahel could influence the precipitation received by the W. Sahel sink region.LEAD INTO NEXT SLIDE: Now that we have seen the boundary for the W. Sahel, lets take a look at the pshedsfor the other six sink regions
- The broad characteristics of thesepsheds are not surprising.The two Chinese psheds are heavily influenced by evaporation from the Eurasian continent, and are consistent with large-scale atmospheric transport (westerly jet).The Pakistan-India pshed is both influenced by Europe as well as the monsoon from the Indian OceanThe Southern African and Argentinian psheds both reflect the easterly movement of air in the Southern HemisphereLEAD INTO NEXT SLIDE: To better understand what the characteristics of each pshed are, a vulnerability analysis was conducted.
- The vulnerability analysis examined Current land-use (using the Anthromes dataset), The intensity of land-use (based on evaluation of current land-use extent and type)otential land-cover changes (collected from the literature)
- This fall, 2012, I will begin a PhD program with Stockholm University, studying moisture recycling, land-use change, and resilienceWill use coupled models to look at consequences of changing vegetation and to what extent precipitation changes with land-use change
- The precipitationshed represented here is the ABSOLUTE pshed which is the region that contributes the largest volumes of preciptiation to the sink region. The largest contributors of precipitation to the West Sahel are the Sahel itself, including a very high amount of local recycling.The shape of the precipitationshed is both expected and interesting. The bottom section extends eastward which is consistent with easterly jet stream in the African tropics, while the tail in the Northern Hemisphere section extends westward, consistent with a westerly jet stream.