Assessing the role of farm-level adaptation in limiting the local economic impacts of more frequent extreme weather events in Dutch arable farming systems.

The expected increase in extreme events frequency is likely to considerably affect future crop productivity. Appropriate adaptation measures in agricultural systems should be identified according to the main climate risks expected in a region and taking into account the role of decisions made at the farm level. Yet, there is limited understanding of the interplay between local production capabilities, regional climatic changes and more general socio-economic conditions. We propose a method that combines local productivity factors, economic factors, crop-specific sensitivity to climatic extremes, and climate change scenarios, to assess future economic impacts of extreme events on agricultural systems. Our assessment is spatially explicit and uses discounted time series of cash flows taking into account expected impacts on yield and crop quality, to estimate changes in the expected net present value of agricultural systems. We also assess the economic feasibility of a portfolio of adaptation measures by considering their initial investments, annual costs, and effectiveness in reducing crop damage. We apply the method to investigate potential economic impacts of extreme events in arable farming systems in the Netherlands in period around 2050. We find that the expected increase in frequency can substantially undermine the economic viability of Dutch arable farming systems. The results indicate considerable differences among regions: some regions are severely impacted by all extremes, while others consistently demonstrate high resilience. Though the exact magnitude of the impacts remains highly uncertain, adaptation measures should nevertheless be regarded as no-regret strategies, since they alleviate both economic impacts and uncertainty around impact magnitude

Evidence for reduced magnetic braking in polars from binary population models

We present the first population synthesis of synchronous magnetic cataclysmic variables, called polars, taking into account the effect of the white dwarf (WD) magnetic field on angular momentum loss. We implemented the reduced magnetic braking (MB) model proposed by Li, Wu & Wickramasinghe into the Binary Stellar Evolution (BSE) code recently calibrated for cataclysmic variable (CV) evolution. We then compared separately our predictions for polars and non-magnetic CVs with a large and homogeneous sample of observed CVs from the Sloan Digital Sky Survey. We found that the predicted orbital period distributions and space densities agree with the observations if period bouncers are excluded. For polars, we also find agreement between predicted and observed mass transfer rates, while the mass transfer rates of non-magnetic CVs with periods ≳3 h drastically disagree with those derived from observations. Our results provide strong evidence that the reduced MB model for the evolution of highly magnetized accreting WDs can explain the observed properties of polars. The remaining main issues in our understanding of CV evolution are the origin of the large number of highly magnetic WDs, the large scatter of the observed mass transfer rates for non-magnetic systems with periods ≳3 h, and the absence of period bouncers in observed samples