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Changes in water pressure at the beds of glaciers greatly modify their sliding rate, affecting rates of ice mass loss and sea level change. However, there is still no agreement about the physics of subglacial sliding or how water affects it. Here, we present a new simplified physical model for the effect of transient subglacial hydrology on basal ice velocity. This model assumes that a fraction of the glacier bed is connected by an active hydrologic system that, when averaged over an appropriate scale, is governed by two parameters with limited spatial variability. The sliding model is reminiscent of Budd's empirical sliding law but with fundamental differences including a dependence on the fractional area of the active hydrologic system. With periodic surface meltwater forcing, the model displays classic diffusion-wave behavior, with a downstream time lag and decay of subglacial water pressure perturbations. Testing the model against Greenland observations suggests that, despite its simplicity, it captures key features of observed proglacial discharges and ice velocities with reasonable physical parameter values. Given these encouraging findings, including this sliding model in predictive ice-sheet models may improve their ability to predict time-evolving velocities and associated sea level change and reduce the related uncertainties.
Do restricting reforms work? We investigate the effects of rules reforms and procedural reforms on districting outcomes. First, we investigate the effects of common “fair districting” criteria – that is, rules that require (or prohibit) certain outcomes in districting. We find little evidence that adding additional criteria will prevent partisan bias in districting. In many cases, such as district compactness requirements, it appears that districting authorities frequently ignore the rules. The biggest drawback with rules-based reforms is that they depend upon the judiciary for enforcement. We then evaluate the effects of “procedural reforms,” like citizen redistricting commissions. We find systemically less bias in districting when the maps are drawn by citizens and other independent bodies. Although the design and mechanics of commissions vary widely, we find the least bias in the maps drawn by redistricting bodies that forbid membership by politicians. This suggests that independent redistricting commissions represent an effective solution against partisan gerrymandering, provided they are staffed by citizens or independent public officials.
What lessons can we draw from the study of 2011 state legislative redistricting? We find that, on the one hand, predicting partisan gerrymandering is relatively simple: gerrymandering occurs when one party can monopolize redistricting and has an incentive to draw biased maps. One the other hand, our investigations of racial segregation and political geography reveal the intimate links between racial gerrymandering and political gerrymandering and suggest that the Republican Party in 2011 was willing to use racial vote dilution in many states in order to achieve extreme bias. We conclude with an assessment of redistricting reforms in Virginia and “best practices” in preventing partisan gerrymandering.
Is partisan gerrymandering widespread in the state legislatures? We assess state legislative redistricting maps approved by state governments in 2011. We find results that are similar to estimates of districting bias in the US House. On average, partisan bias increased after redistricting. State governments approved more than forty state legislative redistricting plans that gave one party an extreme electoral advantage. Although we find a few examples of Democratic gerrymanders with modest levels of bias, most of the extremely biased maps favor the Republican Party. In total, there are nearly two dozen maps that award Republicans 20 percent more of the seats than Democrats when the vote is close. These extreme partisan gerrymanders give Republicans a considerable structural advantage in state legislative elections. We estimate that, in the average state legislative assembly, Republican candidates can expect to win about 9 percent more seats than Democratic candidates would for a given share of the vote, between 45 percent and 55 percent of the vote.
We investigate the impact of Voting Rights Act reforms that have required states to draw “majority-minority” districts and to abandon the use of multimember state legislative districts. Have these changes led to more bias in districting, as is often claimed? Our findings show that Republican bias is not an unavoidable outcome of minority districting. When Republicans are in charge, we often find more bias in states with large and geographically segregated Black and Latinx populations. In this regard, Republican gerrymanderers appear to use majority-minority districting as a tool for creating partisan advantage. But we do not see the same outcomes when Democrats, both parties, or independent actors are in charge. We also find that among the handful of states that still use multimember districts to elect state legislators, the average district magnitude in a state legislature imposes a ceiling on the level of bias achievable. However, when partisans are not in charge, multimember districts do not appear to limit partisan bias. Once again, the key variable in predicting the occurrence of bias in districting is whether or not one party controlled redistricting.
We investigate the political and social consequences of the 2010 election and the gerrymandering that followed. We show that many of the governing parties that drew extremely biased maps also enacted greater restrictions on voter eligibility and ballot access prior to the 2016 presidential election. Furthermore, we find evidence that the level of partisan bias present in state legislatures influenced policy outcomes, distinct from partisan control of the legislatures. Many state legislatures, including those in crucial swing states, have effectively insulated themselves from public accountability at the same time that their constituents face growing public health challenges, such as the COVID-19 pandemic.
We investigate the role of politics in determining whether a map is drawn with partisan bias. We take a systematic look at the processes that states use to regulate the drawing of the lines through case studies and empirical analyses of redistricting outcomes, paying particular attention to one key variable: whether the maps were drawn by politicians. We find that the most biased maps occur in competitive states where politicians from a single party were able to draw the maps without having to work with the minority party. Our examination of the effects of bipartisan districting yields inconclusive results. In some cases, when the redistricting process requires two parties to work together to pass a plan, redistricting authorities draw the maps with low levels of seat–vote responsiveness, presumably as a result of the drawing of “safe seats” to benefit incumbents from both parties. However, in other cases, we do not see this outcome. We do find that, on average, bipartisan districting leads to a preservation of the status quo. In the states where two parties worked together to draw the maps, the level of bias in the post-2011 plans deviated little from the pre-2011 plans.
We illuminate the role that political geography plays in determining districting outcomes. We find that the political geographic features of a state population limit the types of maps that districting authorities are able to draw. When Democrats are highly segregated – for example, in populous urban areas – it is easier for Republicans to draw very efficient gerrymanders and difficult for Democrats to draw plans that give Democrats an advantage. When we estimate the relationship between Democratic clustering in cities and Republican bias, we only see a correlation in the maps that were drawn by Republicans. This correlation does not occur in maps drawn by Democrats, or by independent actors such as courts and citizen commissions. In sum, political geography only leads to a Republican advantage when Republicans are drawing the lines. This underscores an obvious truth about redistricting: the maps do not draw themselves. Rather, humans choose the maps that best serve their personal and political interests.
Although scholars have investigated the effects of redistricting for many decades, surprisingly little is known about the causes of redistricting outcomes. We argue that studying state legislative redistricting in 2011 provides a unique opportunity to identify the theoretical determinants of partisan gerrymandering and assess the political, social, and democratic consequences of bias. We also argue that the story of 2011 redistricting is incomplete without a comprehensive investigation of the causes and consequences of redistricting of state legislatures. Ultimately, our findings reveal the interconnectedness of racial and political gerrymandering and suggest that partisan bias has long-term consequences for public policy and democratic health, yet they also show that it is possible to design redistricting institutions to prevent bias.
In this chapter we consider who gerrymandering harms and how. We start by explaining how Vieth v. Jubelirer (2004) and the revival of gerrymandering after 2010 can be viewed as an attempt to roll back the voting rights revolution of the 1960s. That is to say, it is a fundamental assault on the principle of “one-person, one-vote.” We then consider how the harms of state legislative gerrymandering are different than the harms caused by congressional gerrymandering, given the role of state legislatures in redistricting and regulating elections at all levels. Then we consider the question of who suffers harm produced by partisan gerrymandering. We show that those suffering harm are not only those in gerrymandered districts or identifying with disadvantaged parties, but rather all citizens. Finally, we consider gerrymandering in the context of the broader crisis of faith in democracy and on American federalism.
Since the 1960s, the judiciary has become a key player in redistricting, and litigation has become an increasingly common feature of the decennial redistricting process. How do the courts fare when they draw the lines? We investigate the effects of court intervention in several states where federal and state courts redrew or forced changes to state legislative maps. We find that courts are only a partial solution to the problem of gerrymandering, because judicial actors are minimalistic in their treatment of redistricting and, as incrementalists, have a tendency to avoid extreme change. While the federal courts have been assertive in combatting racial gerrymandering, state courts have had only limited effect on partisan bias when they have been delegated the task of redistricting.