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 Groundwater is withdrawn from the Ozark Plateaus aquifer system (Ozark system) for public supply and for domestic, agriculture (including irrigation and aquaculture), livestock, and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（U.S. Geological Survey）于2014年启动，旨在作为全国地下水可利用性整体评估的子区域，评估美国中部奥扎克高原（Ozark Plateaus）的浅层地下淡水资源。奥扎克研究的目标包括：评估人类活动历史对水位及地下水可利用性的影响，量化当前及未来可能的抽水与气候情景下的地下水资源量，以及评估现有监测网络在优化未来地下水资源预测中的价值。既往研究多聚焦不同时间尺度下的局域地下水流模拟，或是稳态条件下的区域系统模拟。尽管此类研究对其预设的科学问题具有实用价值，但仍需开展瞬态条件下的更大尺度区域系统研究，以全面评估随时间动态变化的水资源状况。本研究聚焦多时空尺度，以探究地下水抽水、储水及水位下降的变化特征。区域尺度可系统呈现系统内水资源来源与需求随时间的演变格局。 本研究区域覆盖美国中部密苏里州、阿肯色州、堪萨斯州及俄克拉荷马州的部分区域，总面积约68000平方英里，涵盖奥扎克高原地貌省（Ozark Plateaus Physiographic Province，简称奥扎克高原），包括塞勒姆高原、斯普林菲尔德高原与波士顿山脉。奥扎克高原含水层系统（Ozark Plateaus aquifer system，简称奥扎克含水层系统）的地下水被广泛用于公共供水、生活用水、农业（含灌溉与水产养殖）、牲畜养殖及非农业用途（涵盖工业、火力发电、采矿与商业用水）。奥扎克含水层系统是奥扎克高原居民的重要饮用水源，公共供水与生活用水合计为该区域最大的地下水消耗类型。 降水是奥扎克含水层系统淡水的最终补给来源，该区域降雨多集中于4、5、6月，且降水量整体自北向南递增。目前，地下水开采量仅占奥扎克含水层系统覆盖区域总用水量的10%，但因其作为公共供水与生活用水的核心水源，仍是至关重要的饮用水资源。2010年，奥扎克含水层系统的地下水开采量达3.8亿加仑/日，约占总补给量的2%。尽管地下水开采在水文收支中占比不高，但由于含水层单元储水能力较低，抽水中心周边可快速形成具有陡峭水位梯度的降落漏斗。 1900年至约1965年，进入与流出含水层系统的水量相对稳定，维持在约130亿加仑/日（Bgal/d）。其中大部分补给水量通过系统内的河道径流排泄，以维持水文收支平衡。随时间变化的储水量变化（由流出量与流入量的差值决定）反映了补给量的巨大波动：若补给量减少，水位将随之下降，导致河道地下水排泄量降低，同时含水层储水量被更多释放；反之，补给量增加时，水位上升，河道地下水排泄量增加，含水层储水量得到补充。尽管1900年至2016年抽水总量整体呈上升趋势，但该趋势与同期储水量变化并无明显相关性。区域尺度上，模拟得到的地下水储水量变化与补给量变化的相关性更强，而非抽水增长。1900年至2016年的平均补给量为116亿加仑/日。开发前至1965年，补给量整体高于平均水平；1965年至约1980年，补给量处于低于平均水平的阶段；1980年至约1988年，补给量再次持续高于平均水平，此后直至2000年代中期，补给量维持在平均或低于平均水平，这一变化趋势也反映在水位动态中。 抽水增长与长期气候变化对奥扎克高原水文系统及地下水可利用性的潜在影响，是该区域社区与资源管理者关注的重点。抽水水量随年度波动，但整体预计将随人口、工业与农业需求增长而适度上升。多数气候模型预测，至本世纪中期，奥扎克高原区域的最低与最高气温将有所升高，尤其在仲春至初秋时段。 本研究设置了三个情景以模拟2016年至2060年的可能未来状况，并评估其对水文系统与水资源可利用性的潜在影响。针对每个情景，均评估了从开发前（1900年）至当前（2016年）及未来45年（2060年）的水位与水文收支组分变化： 1. 基准情景：延续1996年至2016年的平均季节性抽水与补给量数值； 2. 抽水情景：延续1996年至2016年的平均季节性补给量数值，并按照2016年至2060年的历史趋势增加抽水，最高可达1996年至2016年平均季节性抽水量的120%； 3. 通用循环模型（General Circulation Model, GCM）情景：延续1996年至2016年的平均季节性抽水数值，补给量则基于多通用循环模型的气温与降水数据，通过水量平衡模型得到的土壤水储量季节性平均值进行调整。 各情景下的水位下降整体格局相似。至2060年，密苏里州西南部与俄克拉荷马州东北部的水位下降区域与2009年相比仅存在小幅差异。在密苏里州斯普林菲尔德以南的某一区域，基准情景与GCM情景下的水位下降幅度小于2009年，这可能是由于该区域更大比例的用水需求已由地下水转向地表水供应。针对94口实时观测井，各情景下的预测抽水、补给与含水层参数均对水位预测的不确定性具有重要影响。在奥扎克含水层系统的高产中层与下层含水层以及圣弗朗西斯隔水层中，模拟得到的含水层参数对约35%的实时观测井的水位预测不确定性贡献最大。在94口实时观测井中，有82口井设于下层奥扎克含水层中。