On the evening of the 7 August 1996 an intense storm occurred over the Ara s catchment near Biescas in the central Pyrenees. Eighty-seven people were killed as a result of the subsequent¯ood, which hit a campsite located on the alluvial fan at the outlet of the 18 . 8 km 2 catchment. This paper presents the main results of a hydromorphological study of the event. The Bete s subcatchment received the most intense rainfall, estimated at somewhat in excess of 250 mm, which resulted in a peak¯ow from this tributary of 300 m 3 s À1 . Just downstream from the Bete s river junction,¯ow in the main channel reached 400 m 3 s À1 , increasing to around 500 m 3 s À1 further downstream. Rainfall in the larger Aso tributary was less intense, and in the head reaches¯ow remained within-bank, representing a one in two-year return period event.Flow from this tributary did not exceed 100 m 3 s À1 , indicating that the Bete s subcatchment supplied some 75% of thē ow from just 28 . 7% of the catchment area. The extreme¯ows caused the collapse of a series of sediment trap dams in the Ara s channel downstream of the Bete s junction. This resulted in the addition of 68 000 m 3 of sediment to an already disastrous event. Data from other rain gauges in the area showed both the extremely local nature of the event, and the problems of return period analysis for such storms, whose peaks are rarely observed at gauges. Together with the high geomorphological risks of the zone, this leads to the conclusion that a new method of spatial and temporal risk analysis is required for infrastructure planning.

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The Mediterranean is one of the regions of the world where human-induced climate warming is expected to have large impacts on water and environmental resources. To predict shifts in the current climate system, more regional climate records, including seasonal-to-century scale variability spanning longer than the instrumental periods, are needed. To help fill this gap, we provide a reconstruction of autumn precipitation variations for the Central Pyrenees range since 1500 Common Era (CE) using the varved sediments of Lake Montcortès. To assess the suitability of the calcite sublayer width of the sediments of this lake as a proxy for precipitation anomalies, we performed an analysis and smoothing of the temporal structure of the width series, calibration of the new series with the available instrumental climate records, calculation of a transfer function and testing and comparison of the reconstructed series against available empirical data.The prediction model was statistically robust and showed that the climatic signal was captured in the calcite sublayers. The reconstruction provides the first estimations of regional autumn precipitation shifts in the Central Pyrenees at annual resolution, since 1500 CE. Pronounced interdecadal shifts in precipitation were noticeable; no increasing nor decreasing linear trends or periods of extreme precipitation events were identified. The reconstructed precipitation anomalies suggest a decrease in rainfall during the coldest phase within the coldest period of the Little Ice Age and also during the 20th century, probably associated to current Global Warming. Correlations between autumn precipitation and the North Atlantic Oscillation, Western Mediterranean Oscillation and Southern Oscillation indices were weak to moderate. A potential relationship with the Atlantic Multidecadal Oscillation pattern is suggested. The reconstructed autumn precipitation trends are coherent with other palaeohydrological reconstructions in similar Mediterranean settings, and consistent at a regional level.

<p>High mountain lakes are pristine ecosystems that archive in their sediments high-resolution records of watershed and lake evolution. Understanding how they have responded to Holocene climate fluctuations and anthropic impacts provides essential information to put into a historical context the magnitude and unique features of the current global change.</p><p>The REPLIM project funded by the Interreg program (POCTEFA 2014-2020) has implemented a network of lakes in Spain, France and Andorra to study current and past climate, environmental and anthropic changes in lakes. In August 2017, eight short sediment cores were recovered in Montmalús Lake (2433 m a.s.l., Andorra). We present a paleolimnological reconstruction based on sedimentary facies, chemical (main and trace element) analyses and δ<sup>13</sup>C and δ<sup>15</sup>N of bulk organic matter. We developed a robust age model based on <sup>210</sup>Pb, <sup>137</sup>Cs and <sup>14</sup>C dating for the last 2000 years. Moreover, modern lake dynamics have been characterized with continuous water temperature measurements at various depths, periodical water sampling and sediment traps.</p><p>The results show large depositional fluctuations in the lake dynamics, especially during the Little Ice Age, with changes in organic matter accumulation, bioproductivity and sources and increased sediment delivery. Sedimentological and geochemical indicators point to the onset of high human impact in the landscape around the 11<sup>th</sup> century. Also, medieval mining and metallurgic activity from 11<sup>th</sup> to 14<sup>th</sup> centuries increased Pb deposition.</p><p>The 20<sup>th</sup> century is characterized by a recovery in organic accumulation and bioproductivity rates. Heavy metal deposition also increased during the late 20<sup>th</sup> century and started to decrease in the 2010’s decade, without reaching the background values</p><p>This study provides the first data on recent changes in lakes from the Principality of Andorra. The results highlight the uniqueness of current global change impacts in alpine lakes and underline the interplay of Great Acceleration and Global Warming processes in these fragile and sensitive depositional systems.</p>

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