GroMoPo Metadata for Ozark Plateau USGS model

The study described in this report, initiated by the U.S. Geological Survey in 2014, was designed to evaluate fresh groundwater resources within the Ozark Plateaus, central United States, as an area within a broader national assessment of groundwater availability. The goals of the Ozark study were to evaluate historical effects of human activities on water levels and groundwater availability, quantify groundwater resources now and under probable future pumping and climate conditions, and evaluate existing monitoring networks for their value in making better predictions of future groundwater resources. Previous studies include simulation of local-scale groundwater flow under varying temporal scales, or simulation of the regional system under steady-state conditions. While these studies are useful, particularly for the problem for which they were designed, there is a need to look at the larger regional system under transient conditions to fully evaluate the water resource over time. This study focused on multiple spatial and temporal scales to examine changes in groundwater pumping, storage, and water-level declines. The regional scale provides a broad view of the sources and demands on the system with time. The study area covers approximately 68,000 square miles in the central United States in parts of Missouri, Arkansas, Kansas, and Oklahoma and encompasses the Ozark Plateaus Physiographic Province (Ozark Plateaus), including the Salem Plateau, Springfield Plateau, and Boston Mountains. Groundwater is withdrawn from the Ozark Plateaus aquifer system (Ozark system) for public supply and for domestic, agriculture (including irrigation and aquaculture), livestock, and non-agricultural use (including industrial, thermoelectric power generation, mining, and commercial). The Ozark system provides an important drinking-water supply for people living in the Ozark Plateaus because public supply and domestic use combined constitute the largest groundwater use. Precipitation is the ultimate source of freshwater to the Ozark system; most rainfall occurs during April, May, and June, and precipitation increases generally from north to south across the study area. Groundwater use currently accounts for only 10 percent of the total water use in the areas overlying the Ozark system, but provides a critical drinking-water resource because public supply and domestic groundwater withdrawals are largely from groundwater resources. The 380 million gallons per day of groundwater withdrawn from the Ozark system in 2010 accounts for approximately 2 percent of recharge. Although groundwater use represents a small component of the hydrologic budget, because of low storage in aquifer units, cones of depression with steep water-level gradients can develop quickly around pumping centers. The amount of water entering and leaving the aquifer system from 1900 to about 1965 was relatively constant at a rate of about 13 billion gallons per day (Bgal/d). Much of this inflow of water is discharged through streams in the system to balance the hydrologic budget. Changes in storage over time (from outflows to inflows) reflect the large variability in recharge: if recharge decreases, water levels will decrease, resulting in less groundwater discharge to streams and more water released from aquifer storage. Conversely, when recharge increases, water levels increase, more groundwater discharges to streams, and aquifer storage is replenished. Although pumping generally increased from 1900 to 2016, it does not appear to correlate with the change in storage over the same time period. Regionally, simulated change in groundwater storage corresponds with changes in recharge, more so than with increases in pumping. Average recharge was 11.6 Bgal/d for the period 1900 to 2016. Recharge was generally above average from predevelopment to 1965, followed by a period of below-average recharge from 1965 to about 1980. Recharge remained consistently above average from 1980 to about 1988, after which there was a period of average or below-average recharge, reflected by a decline through the mid-2000s. The implications and potential effects of increased pumping and long-term climate change on the Ozark Plateaus hydrologic system and groundwater availability are a concern for communities and resource managers in the area. Pumping varies from year to year, but is generally expected to moderately increase with population, industrial, and agricultural needs. Most climate models predict warmer minimum and maximum air temperatures by midcentury in the Ozark Plateaus area, especially from midspring through early fall. Three scenarios were developed to simulate possible future conditions from 2016 to 2060 and assess the potential effects on the hydrologic system and availability of water resources. For each scenario, changes in water levels and hydrologic budget components were evaluated from predevelopment (1900) to present (2016) and 45 years into the future (2060). The baseline scenario represents an extension of the average (1996 to 2016) seasonal pumping and recharge values. The pumping scenario is an extension of the average (1996 to 2016) seasonal recharge values with increases in pumping following the historical trend for the period 2016-2060 of up to 120 percent of the 1996 to 2016 average seasonal pumping values. The general circulation model (GCM) scenario is an extension of the average (1996 to 2016) seasonal pumping values and variable recharge based on seasonal averages of soil water storage from a water-balance model using temperature and precipitation from multiple GCMs. The general patterns of water-level decline are similar for each scenario. The areas of water-level decline in southwest Missouri and northeast Oklahoma are only marginally different by 2060 from those of 2009. In one area south of Springfield, Mo., water-level declines are less in the baseline and GCM scenarios than in 2009. This may be the result of a transition from groundwater use to surface-water supplies for a larger percentage of the demand in the area. For all three scenarios, forecasted pumping, recharge, and aquifer properties play an important role in determining the uncertainty of water-level forecasts at 94 real-time observation wells. Simulated aquifer properties in the productive middle and lower Ozark aquifers and the St. Francois confining unit of the Ozark system contribute most to predictive uncertainty in water levels at approximately 35 percent of the real-time observation wells. Out of the 94 real-time observation wells, 82 are developed in the lower Ozark aquifer.

本报告所述研究由美国地质调查局于2014年发起，旨在评估美国中部奥扎克高原地区的淡水地下水资源，该地区作为国家地下水可用性广泛评估的一部分。奥扎克研究的目标是评估人类活动对水位和地下水可用性的历史影响，量化当前及未来可能抽取和气候变化条件下的地下水资源，并评估现有监测网络在预测未来地下水资源价值方面的作用。前期研究包括在不同时间尺度下对局部尺度地下水流的模拟，或对稳态条件下的区域系统的模拟。尽管这些研究对于它们设计的问题是有用的，但仍需考察在瞬态条件下的更大区域系统，以全面评估水资源随时间的变化。本研究聚焦于多个空间和时间尺度，以考察地下水抽取、储存和水位下降的变化。区域尺度提供了系统来源和需求随时间变化的广阔视角。研究区域覆盖了美国中部约68,000平方英里的密苏里州、阿肯色州、堪萨斯州和俄克拉荷马州的部分地区，包括奥扎克高原地貌省（奥扎克高原），包括塞勒姆高原、斯普林菲尔德高原和波士顿山脉。地下水从奥扎克高原含水层系统（奥扎克系统）中提取，用于公共供水以及家庭、农业（包括灌溉和养殖业）、畜牧业和非农业用途（包括工业、热电发电、采矿和商业）。奥扎克系统为奥扎克高原居民提供了重要的饮用水供应，因为公共供应和家庭使用共同构成了最大的地下水使用。降水是奥扎克系统的最终淡水来源；大部分降水发生在四月、五月和六月，降水通常从研究区域的北部向南部增加。目前，地下水使用仅占奥扎克系统上覆地区总用水量的10％，但提供了关键的饮用水资源，因为公共供应和家庭地下水抽取主要来自地下水资源。2010年从奥扎克系统抽取的3.8亿加仑/天的地下水约占补给量的2％。尽管地下水使用在水资源预算中只占很小的一部分，但由于含水层单元储存量低，抽水中心周围可以迅速形成陡峭的水位梯度下降的漏斗。从1900年到大约1965年，含水层系统进出水量相对稳定，每天约为130亿加仑（Bgal/d）。其中大部分水流入通过系统中的溪流排放，以平衡水文学预算。储存量随时间的变化（从出流到入流）反映了补给的大幅变化：如果补给减少，水位将下降，导致流向溪流的地下水排放减少，从含水层储存中释放的水增加。相反，当补给增加时，水位上升，更多地下水流向溪流，含水层储存得到补充。尽管从1900年到2016年抽水量一般有所增加，但它似乎与同一时期储存量的变化没有相关性。在区域层面，模拟的地下水储存变化与补给变化相对应，这比抽水量的增加更为显著。1900年到2016年的平均补给量为11.6 Bgal/d。补给量在开发前到1965年一般高于平均水平，随后是从1965年到大约1980年的补给量低于平均水平。1980年到大约1988年，补给量持续高于平均水平，此后出现了一个补给量平均或低于平均水平的时期，这反映在2000年代中期的下降。增加抽水和长期气候变化对奥扎克高原水文学系统和地下水可用性的潜在影响是当地社区和资源管理者关注的焦点。抽水量每年都有所变化，但普遍预计将随着人口、工业和农业需求而适度增加。大多数气候模型预测，到本世纪中叶，奥扎克高原地区的最低和最高气温将变暖，尤其是在从春末到初秋期间。开发了三种情景来模拟2016年到2060年可能的未来条件，并评估对水文学系统和水资源可用性的潜在影响。对于每种情景，从开发前（1900年）到目前（2016年）和45年后（2060年）的水位变化和水文学预算组成部分的变化都进行了评估。基线情景代表了1996年到2016年季节性抽水和补给值的平均值的延续。抽水情景是1996年到2016年季节性补给值的平均值的延续，并且抽水量将根据2016年到2060年历史趋势的增加，达到1996年到2016年季节性抽水平均值的大约120％。一般环流模型（GCM）情景是1996年到2016年季节性抽水值的延续，并根据多个GCM的温度和降水数据，基于水平衡模型中土壤水储存的季节性平均值进行可变补给。水位下降的一般模式在每种情景中都是相似的。到2060年，密苏里州西南部和俄克拉荷马州东北部的水位下降区域与2009年的区域仅略有不同。在密苏里州斯普林菲尔德以南的一个区域，基线和GCM情景下的水位下降比2009年要少。这可能是因为该地区需求中更大比例的地下水使用转向地表水供应。对于所有三种情景，预测的抽水、补给和含水层特性在确定94个实时观测井的水位预测不确定性方面发挥着重要作用。在约35个实时观测井中，模拟的奥扎克系统中生产性中间和下奥扎克含水层以及圣弗朗索瓦限制单元的含水层特性对水位预测的不确定性贡献最大。在94个实时观测井中，有82个位于下奥扎克含水层。