Climate-based Indices Research Articles

Reliability of Moisture Reference Year (MRY) selection methods for hygrothermal performance analysis of wood-frame walls under historical and future climates

Hygrothermal simulations can be used to evaluate the hygrothermal response of building envelope to the effect of climate change. However, to account for the uncertainty in projected future climates, a large number of simulations are required. To reduce computational time, hygrothermal performance of walls is typically evaluated using Moisture Reference Year (MRY), which can be selected based on climate-based indices. This study investigated the reliability of climate-based indices by comparing to the response-based indices obtained from simulations using two methods. Firstly, the direct correlation between two indices is calculated using coefficient of determination (R2). Second method focuses on evaluating the reliability of climate-based indices in ranking the years in terms of moisture severity compared to that based on simulations. Four climate-based indices: Climatic Index (CI), Moisture Index (MI), Severity Index (Isev) and annual WDR and three response-based indices: Mould Index, Moisture Content and RHT index are investigated. In general, R2 between two indices is weak (range of 0–0.79) with highest being 0.79 (between maximum mould index and MI) for stucco cladding wall facing default orientation under historical climate in Calgary. With ranking analysis, the accuracy using climate-based indices in ranking all years is low with some improvement in ranking the first three worst-years. CI and MI perform well and Isev works for north facing walls for cities like Ottawa and Calgary but fails for Vancouver. To have a reliable assessment of moisture risks, further research is needed to improve existing or develop a new climate-based index specific to Canadian climate.

Reliability of Existing Climate Indices in Assessing the Freeze-Thaw Damage Risk of Internally Insulated Masonry Walls

This paper evaluates the reliability of the currently used climate-based indices in selecting a moisture reference year (MRY) for the freeze-thaw (FT) damage risk assessment of internally insulated solid brick walls. The evaluation methodology compares the ranking of the years determined by the climate-based indices and response-based indices from simulations, regarded as actual performance. The hygrothermal response of an old brick masonry wall assembly, before and after retrofit, was investigated in two Canadian cities under historical and projected future climates. Results indicated that climate-based indices failed to represent the actual performance. However, among the response-based indices, the freeze-thaw damage risk index (FTDR) showed a better correlation with the climate-based indices. Additionally, results indicated a better correlation between the climatic index (CI), the moisture index (MI), and FTDR in Ottawa; however, in Vancouver, a better fit was found between MI and FTDR. Moreover, the risk of freeze-thaw increased considerably after interior insulation was added under both historical and projected future climates. The risk of FT damage would increase for Ottawa but decrease for Vancouver under a warming climate projected in the future, based on the climate scenario used in this study. Further research is needed to develop a more reliable method for the ranking and the selection of MRYs on the basis of climate-based indices that is suitable for freeze-thaw damage risk assessment.

The European 2015 drought from a hydrological perspective

Abstract. In 2015 large parts of Europe were affected by drought. In this paper, we analyze the hydrological footprint (dynamic development over space and time) of the drought of 2015 in terms of both severity (magnitude) and spatial extent and compare it to the extreme drought of 2003. Analyses are based on a range of low flow and hydrological drought indices derived for about 800 streamflow records across Europe, collected in a community effort based on a common protocol. We compare the hydrological footprints of both events with the meteorological footprints, in order to learn from similarities and differences of both perspectives and to draw conclusions for drought management. The region affected by hydrological drought in 2015 differed somewhat from the drought of 2003, with its center located more towards eastern Europe. In terms of low flow magnitude, a region surrounding the Czech Republic was the most affected, with summer low flows that exhibited return intervals of 100 years and more. In terms of deficit volumes, the geographical center of the event was in southern Germany, where the drought lasted a particularly long time. A detailed spatial and temporal assessment of the 2015 event showed that the particular behavior in these regions was partly a result of diverging wetness preconditions in the studied catchments. Extreme droughts emerged where preconditions were particularly dry. In regions with wet preconditions, low flow events developed later and tended to be less severe. For both the 2003 and 2015 events, the onset of the hydrological drought was well correlated with the lowest flow recorded during the event (low flow magnitude), pointing towards a potential for early warning of the severity of streamflow drought. Time series of monthly drought indices (both streamflow- and climate-based indices) showed that meteorological and hydrological events developed differently in space and time, both in terms of extent and severity (magnitude). These results emphasize that drought is a hazard which leaves different footprints on the various components of the water cycle at different spatial and temporal scales. The difference in the dynamic development of meteorological and hydrological drought also implies that impacts on various water-use sectors and river ecology cannot be informed by climate indices alone. Thus, an assessment of drought impacts on water resources requires hydrological data in addition to drought indices based solely on climate data. The transboundary scale of the event also suggests that additional efforts need to be undertaken to make timely pan-European hydrological assessments more operational in the future.