water a constraining resource in this semi-desert environment, what
are efficient uses of water in agriculture and in other sectors,
and how vulnerable is the water resource to climate change, development
in other regions of Mexico, and other external factors?
resources are used and influenced by all sectors of human activity.
Experience in many regions of the world illustrate the importance
of conflicts between the competing urban, industrial, and agricultural
sectors as regions develop. In addition, ecosystem and recreation
demands for water are also being added to the mix of demands. In
the Yaqui Basin, the agriculture sector to date has had almost unrestricted
access to water, with little competition from other sectors. Today,
however, growing urban centers, industrial growth, and demands from
outside the Basin suggest that new demands for water are just around
the corner. We plan to explore questions about the vulnerability
of water (and associated agricultural activities) to climate variation
and changing demands in other sectors, and to develop a basis for
decisions about water allocation and use in the Basin.
Water-Resource Planning. While the reservoir system for the
Valley buffers farmers and urban dwellers from variation in precipitation,
long term draw-downs of the reservoirs during drought have at times
had dramatic effects on decisions about cropping systems and management.
Our work to date has indicated almost no long-term planning for
the water system. Recent draw-downs have left little flexibility
for future management decisions. We intend to assess the environmental
(e.g., climate, soil) conditions for which the current allocation
approaches are appropriate, and also how appropriate they are likely
to be for future scenarios of rapid change or increased climatic
conservative management approaches be used to reduce vulnerability?
What are the appropriate allocation decision rules to sustain the
water resource and activities associated with it, and what is the
political and scientific feasibility of establishing such rules?
Can we develop a long-term drought plan? Using long-term records
of precipitation, reservoir volume, and projections for future climate
variation, we will develop decision rules for reservoir water draw-downs
under varying precipitation regimes, and test the consequences of
those models using allocation models developed in our current research.
Interactions. Water availability drives many decisions in agriculture,
including crop selection and fertilization and irrigation strategies.
While the management focus has been on crop and soil performance
under optimal water allocation, there has been little analysis of
how crops perform and soils change under lower water supplies. We
propose to link our water allocation models with agricultural ecosystem
models to explore issues about the consequences of changes in water
allocation and management on crop production and soil degradation
(e.g., increasing salinity), and conversely, the consequences of
crop changes (potentially driven by market forces or other external
factors) for future water supply.
What are the most critical
interactions among water use and soil degradation? How vulnerable
is the valley to degradation and loss of productivity due to salinization?
Our work has suggested that some flexibility in water allocation
can be acquired through use of ground-water resources in combination
with reservoir water (Addams and Gorelick). However, data on the
variable salinity characteristics of the Valley's soils warn of
a need for a decision model that accounts for the soil characteristics
as well as water in deciding the proper mix of surface and subsurface
water for irrigation. Such a decision model is likely to be spatially
explicit. We will work towards an integrated model by combining
GIS-based data on soil characteristics and ecosystem processes with
the spatial water allocation models. For this work, we will utilize
and build on TerraFlux, a spatially determined mathematical model
of ecosystem production and biogeochemical processes with explicit
treatment of soil processes and properties (Asner et al 2001), linked
to the water allocation model now being developed by Steve Gorelick
and Lee Addams.