Watersheds of the Sky

Watersheds of the Skythe 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.

• Evaporation traveling through the atmosphere and falling out as precipitatione.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 precipitatione.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

Moisture Recycling

Terrestrial land surface

Atmospheric

transport

Ocean

Evaporation Precipitation Evaporation

Atmospheric

transport

Water Accounting Model (WAM)van der Ent et al. 2010

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

Terrestrial evaporation dependent water-constrained, rainfed-agriculture

Precipitationshed W. Sahel

E. Sahel precipitationshed

E. China precipitationshed

N. China precipitationshed

Argentina precipitationshed

Pakistan-India precipitationshed

S. Africa precipitationshed

Seven Precipitationsheds

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

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.

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?

Thank you!

Precipitationshed W. Sahel (absolute)

E. China precipitationshed (absolute)

N. China precipitationshed (absolute)

E. Sahel precipitationshed (absolute)

Argentina precipitationshed (absolute)

Pakistan-India precipitationshed (absolute)

S. Africa precipitationshed (absolute)

Backtracking integration