Global sensitivity analysis through polynomial chaos expansion of a basin-scale geochemical compaction model

We present a model-driven uncertainty quantification methodology based on sparse grid sampling techniques in the context of a generalized polynomial chaos expansion (GPCE) approximation of a basin-scale geochemical evolution scenario. The approach is illustrated through a one-dimensional example involving the process of quartz cementation in sandstones and the resulting effects on the dynamics of the vertical distribution of porosity, pressure, and temperature. The proposed theoretical framework and computational tools allow performing an efficient and accurate global sensitivity analysis (GSA) of the system states (i.e., porosity, temperature, pressure, and fluxes) in the presence of uncertain key mechanical and geochemical model parameters as well as boundary conditions. GSA is grounded on the use of the variance-based Sobol indices. These allow discriminating the relative weights of uncertain quantities on the global model variance and can be computed through the GPCE of the model response. Evaluation of the GPCE of the model response is performed through the implementation of a sparse grid approximation technique in the space of the selected uncertain quantities. GPCE is then be employed as a surrogate model of the system states to quantify uncertainty propagation through the model in terms of the probability distribution (and its statistical moments) of target system states.     

Beyond REDD+ readiness: land-use governance to reduce deforestation in Peru

Peru contains the fourth largest area of tropical forest in the world, yet faces a worsening net deforestation rate. In 2008, to address this threat, the national government announced its ambition to reduce deforestation to zero by 2021. Via literature review and key informant interviews, this study assess two years of REDD+ readiness preparations according to six readiness functions. A mixed pattern of outcomes emerge. Although significant advances were made by various local-level initiatives, national-level efforts continue to struggle. Three crucial challenges persist: (1) greater involvement and coordination of ministries and government agencies associated with REDD+ planning, (2) better understanding of deforestation agents and drivers, and (3) integration of REDD+ policies into national and regional plans, which includes clarification of safeguard procedures and design of incentive mechanisms. Integrated land use planning is presented as a platform to foster dialogue that helps to reconcile divergent stakeholder perspectives, coordinate changes to land use, and resolve overlapping land rights.

Policy relevance

This article presents the outcomes of a multi-dimensional assessment of the REDD+ readiness process in Peru. The six key functions in the analytical framework provide the opportunity to evaluate the process in an integrated and systematic manner and highlights the persistence of complex, transversal governance challenges across diverse economic sectors and government agencies. Research findings also reveal a need for policy change and continued investment to ensure success of the national process in Peru. Strong leadership is needed to generate consensus in cross-sectoral negotiations and to establish coordinated land governance and monitoring mechanisms.     

Projection of low flow conditions in Germany under climate change by combining three RCMs and a regional hydrological model

The present study is aimed to: (a) project future low flow conditions in the five largest river basins in Germany, and (b) to account for the projections uncertainties. The eco-hydrological model SWIM was driven by different regional climate models (REMO, CCLM, and Wettreg) to simulate daily river discharges in each study basin. The 50-year low flow was estimated for the period 1961 to 2000, and its return period was assessed for two scenario periods, 2021–2060 and 2061–2100, using the generalized extreme value distribution. The 50-year low flow is likely to occur more frequently in western, southern, and parts of central Germany after 2061, as suggested by more than or equal to 80% of the model runs. The current low flow period (from August to September) may be extended until late autumn at the end of this century. The return period of 50-year deficit volume shows a similar temporal and spatial pattern of change as for the low flow, indicating slightly less severe conditions with lower confidence. When compared with flood projections for the same area using the same models, the severer low flows projected in this study appear more pronounced, consistent, and have lower uncertainty.     

Analysis of current trends in climate parameters,river discharge and glaciers in the Aksu River basin (Central Asia)

Abstract

Climate variability and change play a crucial role in the vulnerable system of the Aksu River basin located in Kyrgyzstan and northwest China, providing precious water resources for the intense oasis agriculture of the Xinjiang Province (China). Ubiquitous warming and increase in precipitation (in the lower part of the basin) have been detected. Glaciers in the region are retreating. Seasonal trends in river discharge show an increase. A clear link could be demonstrated between daily temperature and lagged river discharge at two headwater stations in summer. However, the correlation breaks over short periods in the end of summer or beginning of autumn at the Xiehela station, when the high (over 95th percentile) flow peaks caused by the glacier lake outburst floods of the Merzbacher Lake occur. This feature is a challenge for the climate impact assessment in the region, as these regular outbursts have to be represented in the projections for the future as well.

Editor D. Koutsoyiannis     

Retrieving lateral variations from surface wave dispersion curves‡

Surface wave analysis is usually applied as a 1D tool to estimate V_S profiles. Here we evaluate the potential of surface wave analysis for the case of lateral variations. Lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data. First, an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties. This is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates. Then, a laterally constrained inversion algorithm is adopted to handle 2D effects, although a 1D model has been assumed for the forward problem solution. We have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results. The same procedure, applied to the synthetic data, was then tested on a field case. Both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions.     

泾河上游流域实际蒸散量及其各组分的估算

利用分布式生态水文模型SWIM,基于泾河上游(泾川测站以上) 植被、土壤、气象和水文数据对研究区进行了水文过程的模拟,从而估算了流域的实际蒸散量及其各组分。结果表明：SWIM模型能够较好的模拟泾河上游流域的水文过程,模拟的流域多年(1997-2003 年) 平均实际蒸散量为443 mm,其中土壤蒸发量为259 mm,植被蒸腾量为157 mm,冠层截持量为27 mm。石质山区的森林覆盖区和非森林地的年蒸散总量在整个流域分别具有最大值和最小值,为484 mm和418 mm;黄土区实际蒸散量介于二者之间,平均为447 mm。森林覆盖地区土壤蒸发明显小于其它区域,而蒸腾和冠层截留明显大于其它区域。年内蒸散量主要集中在5-8 月份,占全年总蒸散量的60%,且冠层蒸散比例较大达63%。整个流域湿润年份较干旱年份蒸散量增加了78 mm,其中土壤蒸发增加最多,其次是冠层蒸腾,冠层截留蒸发最小。     

Collisional enhancement of Hi Balmer lines in photoionized nebulae

Collisional excitation of neutral hydrogen atoms can significantly increase the intensity of Balmer lines with respect to pure recombination. If this effect is not taken into account, the abundance analysis of these objects returns biased values, and the bias may be significant if accuracies better than a few percent are required. The most affected objects are young, metal-poor Hii regions, due to their comparatively high temperatures. To date, estimates of collisional enhancement have been based on tailored modeling of individual Hii regions. In this contribution, I describe an ongoing effort to develop a general calibration suitable for application to large samples of objects. Emphasis is placed on the uncertainties affecting the resulting predictions.     

Over 10 years of variation in Mediterranean reef benthic communities

During the last several decades, the Mediterranean littoral shallow water benthic communities have suffered significant changes in their structure and taxa composition. Despite numerous studies conducted to characterize these changes at various levels, it has always been very difficult to disentangle the effects of natural factors from anthropic ones. The main purpose of this work was to evaluate possible changes, over a 10‐year scale, in diversity and abundance of the most representative species of the benthic communities considered to be primarily and potentially affected by natural stressors in a highly protected area. Sets of macro‐photographs were taken in 2002–2003 of three sites inside a small bay called Ca’ dell'Oro, which is the “no entry—no take” zone of the Marine Protected Area of Portofino, in order to analyse the structure of the benthic communities at different depths over a short time scale. The same sampling was repeated 10 years later in 2013. In the 10‐year span, a significant change in the macroalgal coverage and composition was observed, while the overall richness and coverage of species remained almost unchanged. This process resulted in a significant reduction of the habitat complexity of the three‐dimensional algal components. Likewise, a remarkable change in terms of presence and abundance occurred among all zoobenthic components. The benthic communities seem to have suffered from detrimental effects probably caused by climatic events that have been occurring in recent years in the Ligurian Sea.