Impacts of hydrological droughts are profoundly local – to understand and manage affected groundwater resources, monitoring networks must be local as well
The National Oceanic and Atmospheric Administration reports that the climatological community, following the work of Wilhite and Glantz1, recognizes four types of drought:
- meteorological drought
- hydrological drought
- agricultural drought, and
- socioeconomic drought.
The first three are physical phenomenon, whereas the last deals with drought in terms of supply and demand, and its manifestation in socioeconomic systems. Droughts are extensively studied and monitored by industry, academe, and governmental agencies, greatly driven by interest in the socioeconomic impacts.
A hydrological drought is characterized by water supply that is persistently low relative to historic norms – especially in streams, reservoirs, and shallow aquifers. Though droughts originate from abnormally low precipitation, the evolution from meteorological drought to hydrological drought is the result of complicated water cycle processes. Because of this, not all meteorological droughts will lead to hydrological droughts – a meteorological drought can begin and end rapidly before that precipitation deficit can affect local hydrological resources. A hydrological drought will typically take much longer to develop and then recover than a related meteorological drought.
Groundwater Drought – local monitoring is fundamental
Drought in shallow groundwater can be viewed as a specific subset of hydrological drought – groundwater drought is characterized by groundwater levels that are persistently below the long-term average, resulting in reduced saturated thickness and availability. During a groundwater drought, water withdrawals from the shallow aquifer for irrigation, municipal, industrial, and other purposes will likely continue and may increase – this is a human influence that can amplify the meteorological drivers.
The saturated thickness and availability of a groundwater resource at any point in time is best determined by an appropriately dense (spatially and temporally) network of wells that monitors the depth to the water table. However, there is limited spatial coverage of monitoring wells and networks across the country with which to observe and quantify groundwater droughts. The U.S. Geological Survey operates the Climate Response Network, designed to portray the effect of droughts and other climate variability on groundwater levels in shallow confined or unconfined aquifers. However, this national network includes 684 monitoring points – points whose spatial distribution appear to be skewed to the eastern US.
The value of the Climate Response Network for portraying effects at the state and regional scale is clear, but because the socioeconomic impacts of groundwater droughts are profoundly local, the monitoring networks designed to understand and manage these impacts must be local as well. Managing through the socioeconomic impacts of a groundwater drought that has reduced saturated thickness and availability of a critical groundwater resource, requires a density of data that is appropriately local.
Central Texas – the power of local, dense data
A monitoring network that clearly shows the local impact of a groundwater drought is demonstrated in hydrographs from four residential pumping wells located in the same residential development in Central Texas (Figure 1). The water level in this shared aquifer trends lower in these wells through late August or so and then a partial recovery through the end of the year is visible. This particular groundwater drought coincides well with a documented meteorological drought, but that is not always the case. These data demonstrate a local consistency in the drought effect that is important for characterizing the groundwater drought and for defining potential management responses.
The appropriate spatial density of any network designed to monitor saturated thickness and availability in the context of groundwater droughts will be influenced by local hydrogeological and water-use considerations. Water management that occurs at the county, township, or village scale, will have priorities for monitoring that should be reflected in the spatial scale and character of their network. Figure 2 is a map of a monitoring network in Eastern Wisconsin that is well suited for capturing the local village-scale impact of a drought on the groundwater resource. In addition, because a fair number of the monitored wells are close to local streams and lakes, this network will be particularly useful in relating lower levels in the shallow aquifer to changes in baseflow contribution to the surface-water features. Thus linking a local groundwater drought more broadly to the local hydrological drought.
The impacts of hydrological droughts and associated groundwater droughts are often felt most profoundly by local communities and businesses. Monitoring of groundwater levels is fundamental to recognizing and understanding groundwater droughts, and for local communities to define and plan for management responses.
A Wellntel network is the perfect platform on which to design and implement local groundwater-monitoring programs and to enable local experts to identify and quantify groundwater droughts and to manage the impacts.
Contact Wellntel’s VP/BD Charles Dunning, PhD to learn more about Wellntel networks, groundwater science, and groundwater droughts.
1Wilhite, D.A.; and M.H. Glantz. 1985. Understanding the Drought Phenomenon: The Role of Definitions. Water International 10(3):111–120.