Climate change is causing spatial and temporal variations in rainfall in much of the U.S. An increase in storm intensity (particularly in summer months) has been observed in MD and other regions of the U.S, These increases may be associated with increases in mean annual precipitation, but extreme event magnitude is increasing more rapidly than mean annual precipitation. Precipitation concentration (seasonal or storm) can affect both floods and droughts. Intense, short-term drought (flash droughts) are driven by 30-60 days with little water combined with high temperatures that can drive significant decreases in streamflow and agricultural production.
As climate changes, towns and cities with infrastructure built to store, convey, or withstand extreme storms are or will become unsuited for these tasks. Forests in urban areas evapotranspire most summer precipitation, which creates subsurface storage for storm events, particularly for late summer to early fall storms (tropical storm and hurricane season). Groundwater recharge periods are primarily in the fall and winter. Changes in amounts and timing of precipitation could affect stream baseflow and possibly water resource issues for cities like Baltimore, College Park, and Washington D.C. that rely on rivers as water sources. Our current understanding of risk associated with floods and droughts is based on the previous 100+ years of record. With changes in storm and drought intensity, these databases and the statistics they provide are less useful in the prediction of future events and risks. An increase in stormwater runoff, particularly from urban areas, can also carry high water levels to downstream estuaries. Convergence of storm surge, sea-level rise, and river flood levels in coastal urban areas can significantly increase flood risks.
Activities
Due to climate change, a statistical understanding of past storms and droughts is not sufficient to plan for the future. We require a better understanding of spatial and temporal variations in hydrological processes in the Maryland watersheds where people live and where food and forests grow. This includes:
- A better understanding of storm runoff production in both urbanized and non-urban watersheds. In particular, we need to understand spatial variations in water storage capacity within watersheds (target 1 above) and to use that information in watershed management and stormwater mitigation.
- A better understanding of groundwater recharge, stream baseflow, and how they are linked to evapotranspiration (ET). In Maryland, a large proportion of summer precipitation is transpired back to the atmosphere by crops and forests. Our understanding of spatial and temporal variations in ET demand is poor. We can obtain direct measurements of ET into the atmosphere from flux towers, but we can also obtain excellent data on groundwater recharge, storage, etc. from plot and catchment data on soil depth, permeability, soil moisture, plant rooting depths, and the distribution of subsurface storage. These data can come from analysis of watershed data, seismic and other geophysical studies, soil sampling, and modeling. By better understanding water balances, there is an exciting potential that solutions to stormwater runoff problems might also provide solutions to groundwater recharge problems. This would require working with communities to identify where storm runoff is a problem, where there are opportunities for subsurface storage and groundwater recharge. This topic is also linked to water quality and salinization issues, which may limit the use of stormwater runoff.
Engagement with Stakeholders
Stakeholders include planning agencies at the State, County, and Municipal level. This work would build on and greatly expand existing relationships with stakeholders at Maryland Department of the Environment, Maryland Department of Natural Resources, and Washington Metropolitan Council of Governments. Stakeholders also include the Army Corps of Engineers (we work on precipitation and baseflow issues with the Hydrological Research office in D.C., Maryland Dept. of the Environment, the U.S. Geological Survey, and other agencies. Collaboration of people working with hydrological data, hydrological and statistical models, integrated with field data collection, including the use of geophysical and remotely sensed data could provide significant resources to evaluate problems and potential solutions.
Products and Tools
We have been working on tools to better quantify temporal concentration of precipitation and have been using recent data to map changes in precipitation concentration throughout the U.S. We could use higher resolution data to evaluate these changes in Maryland. Precipitation concentration data provide information on periods with high precipitation and periods with precipitation gaps. We are evaluating time periods with precipitation gaps in various parts of Maryland (forests, urban landscapes, etc.) to address how these gaps in precipitation translate to changes in baseflow runoff, groundwater recharge, etc., These data can also be mapped to evaluate potential risks to water resources. Our goal would be to provide tools that could be used to anticipate short term and long-term changes in floods and water supply. In the long term, these changes could include forest management, if existing tree species become less adapted to prevailing climates, with a goal of better understanding possible adaptations to climate change in both urban and forested watersheds.
