Intercomparison of UAV platforms for mapping snow depth distribution in complex alpine terrain

[EN]Unmanned Aerial Vehicles (UAVs) offer great flexibility in acquiring images in inaccessible study areas, which are then processed with stereo-matching techniques through Structure-from-Motion (SfM) algorithms. This procedure allows generating high spatial resolution 3D point clouds. The high accuracy of these 3D models allows the production of detailed snow depth distribution maps through the comparison of point clouds from different dates. In this way, UAVs allow monitoring of remote areas that were not achievable previously. The large number of works evaluating this novel technique has not, to date, conducted a systematic evaluation of concurrent snowpack observations with different UAV devices. Taking into account this, and also bearing in mind that potential users of this technique may be interested in exploiting ready-to-use commercial devices, we conducted an evaluation of the snow depth distribution maps with different commercial UAVs. During the 2018-19 snow season, two multi-rotors (Parrot Anafi and DJI Mavic Pro2) and one fixed-wing device (SenseFly eBee plus) were used on three different dates over a small test area (5 ha) within Izas Experimental Catchment in the Central Pyrenees. Simultaneously, snowpack distribution was retrieved with a Terrestrial Laser Scanner (TLS, RIEGL LPM-321) and was considered as ground truth. Three different georeferencing methods (Ground Control Points, ICP algorithm over snow-free areas and RTK-GPS positioning) were tested, showing equivalent performances under optimum illumination conditions. Additionally, for the three acquisition dates, both multi-rotors were flown at two distinct altitudes (50 and 75 m) to evaluate impact on the obtained snow depth maps. The evaluation with the TLS showed an equivalent performance of the two multi-rotors, with mean RMSE below 0.23 m and maximum volume deviations of less than 5%. Flying altitudes did not show significant differences in the obtained maps. These results were obtained under contrasted snow surface characteristics. This study reveals that under good illumination conditions and in relatively small areas, affordable commercial UAVs provide reliable estimations of snow distribution compared to more sophisticated and expensive close-range remote sensing techniques. Results obtained under overcast skies were poor, demonstrating that UAV observations require clear-sky conditions and acquisitions around noon to guarantee a homogenous illumination of the study area.This work was supported by the research projects of the Spanish Ministry of Economy and Competitiveness projects "El papel de la nieve en la hidrologia de la peninsula iberica y su respuesta a procesos de cambio global-CGL2017-82216-R" and the JPI-Climate co-funded call of the European Commission and INDECIS and CROSSDRO which are part of ERA4CS, and ERA-NET. Authors do not have any conflict of interest.). J. Revuelto is supported by a "Juan de la Cierva Incorporacion" postdoctoral fellow of the Spanish Ministry of Science, Innovation and Universities (Grant IJC2018-036260-I). I. Vidaller is supported by the Grant FPU18/04978 and is studying in the PhD program in the University of Zaragoza (Earth Science Department)

Landforms of the lower Hushe Valley (Central Karakoram, Pakistan)

This paper presents a new geomorphological map for the lower Hushe Valley (below 3400 m asl), located to the SE of the Central Karakoram in Baltistan (North Pakistan). Fieldwork and remote sensing were combined to improve understanding of the most recent surface landforms to produce a 1:50,000 scale map. Thirteen landform types associated with glacial, fluvial, gravitational and mass wasting processes were identified and mapped. Particular emphasis was made on currently dynamic processes that could pose a threat to the population. The distribution of the landforms on the valley (reworked tills, alluvial fans, rockfalls, among others) differs between the eastern and the western hillslopes, and from north to south, mainly due to bedrock types, location of geological structures and distribution of lateral tributaries. This map is the first and necessary step towards a deep assessment on geological risk related to external processes in the area.This research was funded by the Basque Government (Eusko Jaurlaritza) through the Humanitarian Action 2018 fund (PRE2018EH/0004) and the Consolidated Research Group IT1029-16. We also thank the University of the Basque Country UPV/EHU for the suppor

2030 Agendako helburuetatik lurra-ura hartzera

The 2030 Agenda includes objectives in three dimensions (economic, social and environmental). To these three, we must add the territory where the action plans are implemented. Hence, as researchers working in hydrology we must generate knowledge towards the resilience of dynamic territories combining Water and Land. Thus, this article analyses the need to establish a basin-perspective in water management instead of the usual river-perspective, considering the basin as the basic bio-physical unit for territorial planning. Climate change mitigation and adaptation policies converge in the basin, facilitating the identification of synergies and trade-offs between both strategies. In fact, global mitigation policies focus, largely, on carbon sequestration through reforestation, neglecting its side-effects on adaptation. The hydrological functions of the territory affect the quantity, quality, location and timing of water, by accumulating, moving and transforming it. Therefore, accepting this water regulatory function would imply a change in the way of understanding the management of water resources and an improvement in the integration of hydrological services in the territorial planning. For this purpose, local knowledge and knowledge on trade-offs and synergies between different objectives are needed. In this era of uncertainties, we should focus our main research strategies towards minimization of uncertainties in order to properly manage them and make knowledge-informed decisions, thus, changing the management paradigm. We need, therefore, socio-political will to redirect territorial dynamics, incorporating a development model adapted to local ecosystem services limitations, placing Land and Water in the centre of the territory, anywhere in the world; Garapen Iraunkorrerako 2030 Agendaren hiru dimentsioei (ekonomikoa, soziala eta ingurumenarena) lurraldearena gehitu behar zaie, ekintza-planak gauzatzeko ezinbesteko ingurune fisikoa baita. Hortik dator hidrologiatik ari garen ikertzaileok iraunkortasunari egin diezaiokegun ekarpena: ura eta lurra uztartuta lurralde dinamikoak erresiliente egiteko bidean ezagutza sortzea, erabakietan eragiteko. Iraunkortasuna zutabe hartuta, uraren kudeaketan ohikoa den ibai-ikuspegia aldatu eta arro-ikuspegia ezarri beharra dugu, eta ibai-arroa (ura + lurraldea) lurralde-antolamenduaren oinarrizko unitate biofisiko bihurtu. Hala, klima-aldaketaren aurrean ezartzen diren arintze- eta egokitze-politiken bateragune bihurtzen da ibai-arroa, bi estrategia horien arteko sinergiak eta helburu-gatazkak identifikatzea errazten duen heinean. Izan ere, klima-aldaketarekin lotutako mundu mailako arintze-politiken oinarriak karbonoa bahitzea eta horri lotuta lurraldea basotzea dira neurri handi batean, basotzeak klima-aldaketara egokitzeko ekar ditzakeen albo-kalteak kontuan izan gabe. Lurraldearen funtzio hidrologikoek eragina dute uraren kantitatean, kalitatean, kokapenean eta denboran, zeren eta ura metatzen, mugitzen etaeraldatzen baitute. Beraz, lurraldeak uraren erregulatzaile gisa duen funtzioa onartuz gero, baliabide hidrologikoen kudeaketa ulertzeko modua aldatuko litzateke, baita egokitzera bidean lurraldearen kudeaketan zerbitzu hidrologikoak barneratzea erraztuko ere. Horretarako, beharrezkoa da tokiko eskalari lotutako ezagutzen eta helburuen arteko gatazkak eta sinergiak zein diren jakitea. Alde horretatik, bizi dugun ziurgabetasun-aroan, auzi horiek argitzera bideratu behar genituzke ikerketa-bide nagusiak, haiek egoki kudeatzeko eta ezagutzak informatutako erabakiak hartzeko, ohiko inertziak gaindituta, kudeaketa-paradigma aldatuta. Hortaz, lurralde-dinamikak birbideratzeko borondate soziopolitikoa behar da, eta naturak lekuan-lekuan eskaintzen dituen zerbitzu ekosistemikoen mugetara egokituriko garapen-eredu bat barneratu, lurra eta ura lurraldearen ardatzean jarrita, munduko edozein herrialdetan

Toward an Ice-Free Mountain Range: Demise of Pyrenean Glaciers During 2011-2020

[EN]Pyrenean glaciers are the largest in southern Europe. Their survival is threatened by climate change, highlighting the significance of their study. This research presents an assessment of changes in the glacierized area and thickness of Pyrenean glaciers from 2011 to 2020, using high-resolution optical satellite, airborne lidar and UAV images. The total glacierized area has shrunk by 23.2% and thickness has decreased on average by 6.3 m. These two variables show no correlation for individual glaciers. Although climatic conditions do not vary much among glaciers, their evolution was heterogeneous during the study period. The smaller glaciers (10 ha) have a more homogeneous response. This can be attributed to the generally larger influence of local topography on the response of the smaller Pyrenean glaciers. There is no sign of slowdown in glacier shrinkage respect to previous decades.This work was supported by the Interreg-POCTEFA project OPCC ADAPYR and Spanish Ministry of Economy and Competitiveness project "CGL2017-82216-R." J. Revuelto is supported by the Grant IJC2018-036260-I. I. Vidaller is supported by the Grant FPU18/04978 and is studying the PhD program in the University of Zaragoza. E. Izagirre and I. Rico are supported by the Grant PPGI19/02 (UPV/EHU) and the Consolidated Research Group IT1029-16 (Basque Country Government). E. Berthier acknowledges support from the French Space Agency (CNES)