*4.8. Nested Enterprises*

Rules for developing and implementing IMPs are nested within provisions of the GWMPA. [2] saw the volatility of climate as a common characteristic across multiple CPRs. However, [27] reflect on the absence of environmental accounting within Ostrom's CPR

design principles. In our case, the changes in ground water levels and recharge in three NRDs encompass the complexities of interdependent hydroclimate, water management, and soil physical properties [6,7,28] used crops' evapotranspirative demands, rainfall, and streamflow as variables that integrate irrigation management, rainfall variability, and soil infiltration capacities. These observed data were inputs to a data-driven model developed that successfully reproduces the changes in groundwater well-levels. Thus, the difference among Figure 3A–C can represent the differences in water governance across UPB's NRDs. For example, consistent depletion of groundwater levels in NRD-1, -2, and -3 (2, 4 and 5 m, respectively) started in 2002 indicate how consistent streamflow withdrawals affect aquifer recharge. On the other hand, inflections in the negative trends that occurred in 2005 and 2007 in the NRD-1 and the NRD-2, respectively, illustrate how changes in diverted excess of river flows increase aquifer recharge. In comparison, the rise in ground water well levels in the NRD-1 (2 m) responds to the agreemen<sup>t</sup> among the NRDs, irrigation districts, and NeDNR. In locations like the NRD-2 and NRD-3, the less conspicuous rise (<1 m) may be attributed to intraseasonal increments in rainfall. Depletion of ground water depth after 2012 can be attributed to droughts. The 2012 flash drought reported by [29] was evident in NRD-1, -2, and -3.

**Figure 3.** Interannual changes of integrated (surface and sub-surface) hydrological responses in three Natural Resources Districts. ( **A**) illustrates NRD 1; (**B**) illustrate temporal changes in groundwater well levels in NRD 2; and ( **C**) illustrate temporal changes in groundwater well levels in NRD 3. The location of the NRD is not disclosed due to security constrains.

The GWMPA, its IMP process, and data on variations in hydrological connectivity across the UPB provided the background for this study. Nebraska's decentralized framework in which each NRD develops an IMP based on its unique conditions, is consistent with Ostrom's "bottom-up" approach to the managemen<sup>t</sup> of common pool resource institutions, although this study makes no claim that following Ostrom's design principles is a predictor of successful outcomes. As [30] point out, they are relevant for simple common pool resources, but additional research is needed in more complex social-ecological systems. Conditions in the UPB are more complex than the small-scale irrigation districts that were the focus of Ostrom's original work. Nevertheless, these design principles can work as a heuristic device—helping to focus on key elements in common pool resource managemen<sup>t</sup> like surface and ground water having a hydrological connection.

Common pool resource principles help to explain why it is in the collective interest of actors to decrease the likelihood of exploiting and exhausting resources, thereby obtaining long-term benefits for all [2]. The emphasis in Ostrom's original work was on processes of local self-governance in small-scale situations. As [31] point out, however, Ostrom recognized that when local common pool resources are part of larger systems, the organizations that govern them are more successful when linked in a nested fashion, that is, when actors at different scales share rules or strategies through formal means. Following [31], we argue that Ostrom's design principles can be used to examine the IMP process in Nebraska.
