Climate change can cause droughts and floods and highlights the need to improve our understanding of water budgets in Indiana. During dry periods of low precipitation, the hydrologic cycle shifts into a deficit phase. Water is lost from the landscape due to several processes such as transpiration by plants, and by evaporation from streams, rivers, and lakes. Alternatively, during periods of excessive precipitation where rainfall exceeds recharge into soil, overland flow can lead to nutrient and soil runoff and flooding. Better critical zone monitoring of water mobility can therefore lead to enhanced models for seed and fertilizer application, soil moisture predictions for plant growth and production, groundwater flow models for minimum flow levels and extraction estimates, and hydraulic routing calculations for timing and duration of floods. Researchers at the Indiana Geological and Water Survey therefore developed the IWBN to monitor trends in water loss and gain in the hydrologic cycle across a range of climates, soil types, land use, and physiography (fig. 1).
\r\nFigure 1. Major surface and atmospheric components of the hydrologic cycle. (Source: National Oceanic and Atmospheric Administration)
\r\n\r\n In hydrogeology, the continuity equation (i.e., water balance) is a fundamental accounting procedure to predict streamflow, soil moisture, and groundwater availability. Monitoring the input and output of water at a site can help us plan and prepare for floods and droughts. At a local scale, the water balance can help to determine storage for stormwater and irrigation, refine best management practices on watersheds, and enhance the management of wetlands, ponds, and lakes. At the larger scale, water balance assessments can help us model the volume of water in streams, rivers, lakes, and aquifer systems. Effective water resource planning requires long-term data to evaluate trends in watersheds aquifers. The IWBN provides these data across a range of historical hydrologic and climate conditions at a suite of representative sites.\r\n
\r\n \r\nIndiana farmers face challenges arising from weather-driven uncertainty. Access to quality weather, soil, and groundwater level data allows them to plan accordingly to maximize yields. IWBN sites with rigorous quality control protocols provide information for farmers who lack field-scale instrumentation and reference data for comparison/validation. For example, soil temperature data provide guidance for spring planting and frozen-ground conditions that impact nutrient runoff. Soil moisture data at nearby stations offer a proxy for field drying conditions following rain events and allow farmers to normalize yield gain/loss with growing conditions.
\r\nWeather forecasters and local decision-makers need information about storm events that bring heavy precipitation and strong winds to communities. Predicting these weather phenomena requires high-resolution models, and there is an emerging shift toward regional climate models to address these concerns [1]. The development and calibration of high-resolution weather and climate simulations require quality data related to mesoscale weather and landscape conditions, such as those data collected by statewide Mesonets [2]. Monitoring efforts such as the IWBN strive to capture conditions beyond the \"backyard scale\" that might not be representative of conditions throughout a county or region within the state.
\r\nMeasurements by the IWBN compile data on Indiana's water balance and make those data available to users on a timely basis. Furthermore, quality control protocols are established, and quality assurance measures are in place to identify any limitations associated with specific observations.
\r\nThe IWBN standard components include:
\r\nEvapotranspiration is a hydrologic parameter that characterizes the combined vaporization of water leaving the earth's surface by ground evaporation and plant transpiration processes. Meteorological factors determining evapotranspiration are weather parameters that provide energy for vaporization, thus removing water vapor from the evaporating surface [3]. These weather parameters and rainfall measurements are monitored as part of the IWBN, which are essential for quantifying atmospheric inputs to the hydrologic system at each monitoring site.
\r\nThe sensible heat of ambient air transfers heat to vegetation and, by doing so, exerts a controlling influence on evapotranspiration rates while the water vapor pressure at the evapotranspiring surface and the surrounding air, established by measuring local relative humidity, is the determining factor for vapor removal [3]. Air temperature and relative humidity sensors are placed 1.5 to 2.5 m (4.9 – 8.2 ft) above ground in naturally aspirated louvered shields to minimize radiational heating and cooling biases. The standard shields used at IWBN monitoring sites are ten-fin shields that house combined air temperature and relative humidity probes mounted vertically within the shields.
\r\nSolar radiation is the most significant energy source driving the vaporization of liquid water at the earth's surface by evaporation and plant transpiration [3]. Incoming shortwave solar radiation is measured using silicon-cell pyranometers that are mounted on the south side of monitoring station masts to minimize obstructions by the instrumentation platform. The sensors are generally mounted 2.5 m (8.2 ft) above ground.
\r\nPrecipitation in the form of rainfall is measured using tipping bucket rain gauges at each IWBN monitoring site. The tipping bucket catch orifices are 15.4 cm (6.1 in) in diameter and calibrated to record 0.254-mm (0.01-in) intervals of rainfall with each activation of the tipping mechanism.
\r\nWind and air turbulence transfer large quantities of air over evaporating surfaces and are primary mechanisms for vapor removal. The air above the evaporating surface becomes gradually saturated with water vapor and must be replaced with drier air to sustain elevated evapotranspiration rates [3]. Wind anemometers (measuring wind speed) and vanes (measuring wind direction) are placed 2.5 to 3.5 m (8.2 – 11.5 ft) above ground at IWBN sites.
\r\nAtmospheric pressure changes play a relatively minor role in controlling evapotranspiration rates [4]. However, this weather parameter is an essential component for mesonet-scale monitoring to facilitate improved forecasting and understand of weather and climate patterns.
\r\nSoil moisture is a critical land surface variable that impacts a wide variety of climate and agricultural applications, from agricultural monitoring to weather prediction to drought and flood forecasting [5]. Soil moisture is most commonly expressed as soil volumetric water content (VWC), which is the ratio of water volume to total soil volume for the soil volume being measured. One challenge associated with interpreting soil volumetric water content from one location to the next is that these observations are strongly dependent on soil physical properties (for example, soil texture, density, and texture).
\r\nSoil moisture is monitored at all IWBN sites at a standard 10-cm (4-in) depth using multiparameter soil sensors that measure soil VWC, temperature, and electrical conductivity. The recorded VWC observations are temperature-corrected to account for temperature influences that can affect measurements.
\r\nSoil temperature data are essential for understanding root-zone planting conditions, frozen ground impacts on flooding, infiltration patterns, and ground-source heat pump efficiencies for heating and cooling purposes.
\r\nThe focus of IWBN groundwater monitoring is to assess long-term water-level trends and seasonal variations for monitoring wells categorized as \"trend\" monitoring sites in the National Groundwater Monitoring Network (NGWMN) framework document [6]. Since 2016, data from IWBN groundwater monitoring wells have been compiled and submitted to the NGWMN, a cooperative program that integrates data from local and state monitoring networks with a nationwide database hosted by the U.S. Geological Survey. The primary focus of this program is to collect data for regional water-supply aquifers. Shallow groundwater conditions are also monitored at several IWBN sites, and such data are essential for understanding surface water and groundwater interactions that control flood timing and duration, as well as understanding dynamics of seasonal high water tables that have economic impacts during spring planting conditions. These impacts may become more prevalent under future climate change.
\r\nContinuous groundwater-level data are collected using both vented and nonvented pressure transducers. Vented transducers have a pressure-sensing membrane connected to the atmosphere via a tube running the length of the sensor cable that provides immediate compensation for barometric effects. Nonvented pressure transducers require a separate barometric pressure sensor to facilitate postprocessing that removes atmospheric effects on water-level data.
\r\nGroundwater temperature data are essential for understanding the potential long-term effects of global warming on groundwater resources, evaluating and designing geothermal heat-pump systems, and understanding groundwater flow paths [7]. Both vented and nonvented pressure transducers commonly contain coupled thermistors as part of the sensor.
\r\n\r\n [1] Gutowski, W.J., Ullrich, P.A., Hall, A., Leung, L.R., O’Brien, T.A., Patricola, C.M., Arritt, R.W., Bukovsky, M.S., Calvin, K.V., Feng, Z. and Jones, A.D., 2020, The ongoing need for high-resolution regional climate models–process understanding and stakeholder information: Bulletin of the American Meteorological Society, v. 101, no. 5, p. E664–E683.
\r\n\r\n [2] Brock, F. V., Crawford, K. C., Elliott, R. L., Cuperus, G. W., Stadler, S. J., Johnson, H. L., & Eilts, M. D., 1995, The Oklahoma Mesonet–a technical overview: Journal of Atmospheric and Oceanic Technology, v. 12, no. 1, p. 5–19.
\r\n\r\n [3] Allen, R. G., Pereira, L. S., Raes, D., & Smith, M., 1998, Crop evapotranspiration–guidelines for computing crop water requirements: FAO Irrigation and Drainage Paper 56. FAO, Rome, v. 300, no. 9, p. D05109.
\r\n\r\n [4] Jarraud, M., 2020, Guide to meteorological instruments and methods of observation (WMO-No. 8): Geneva, Switzerland, World Meteorological Organisation, v. 29.
\r\n\r\n [5] The National Soil Moisture Network Community, 2020, A strategy for the National Soil Moisture Network–coordinated, high-quality, nationwide, soil moisture information for the public good, p. 4.
\r\n\r\n [6] The Advisory Committee on Water Information, 2013, A national framework for groundwater monitoring in the United States: U.S. National Groundwater Monitoring Network, p. 170.
\r\n\r\n [7] Anderson, M. P., 2005, Heat as a groundwater tracer: Groundwater, v. 43, no. 6, p. 951–968.
\r\nFor more information contact the IGWS (igwsinfo@indiana.edu)
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