Evaluation of long-term changes in precipitation over Bolivia based on observations and Coupled Model Intercomparison Project models

Using observations and model simulations from the 5th and 6th phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively), this study evaluated changes in monthly, seasonal, and annual precipitation over Bolivia from 1950 to 2019. Results demonstrate that observed precipitation is characterized by strong interannual and decadal variability. However, long-term precipitation trends were not identified on the annual scale. Similarly, changes in seasonal precipitation were almost nonsignificant (p > .05) for the study period. Spatially, albeit with its complex orography, no substantial regional variations in observed precipitation trends can be identified across Bolivia. In contrast, long-term precipitation trends, based on CMIP5 and CMIP6 models, suggest a dominance of negative trends, mainly during austral winter (JJA) (−10%) and spring (SON) (−15%). These negative trends were more pronounced in the lowlands of Bolivia (−20%). Overall, these contradictory results highlight the need for validating precipitation trend outputs from model simulations, especially in areas of complex topography like Bolivia.This work was sup-ported by the research projects CGL2017-82216-R,PCI2019-103631, and PID2019-108589RA-I00, financedby the Spanish Ministry of Science and FEDER, theCROSSDRO project financed by the AXIS (Assessment ofCross(X)-sectorial climate impacts and pathways for Sus-tainable transformation), the JPI-Climate co-funded callof the European Commission, and the LINCGLOBAL-CSIC project (INCGLO0023, RED-CLIMA)

Conexión entre los patrones de circulación atmosférica del Atlántico Norte y la variabilidad de la precipitación invernal en la Península Ibérica

Las proyecciones climáticas más avanzadas indican, con alta confianza, un incremento de la frecuencia, persistencia y severidad de los periodos secos en el sur de Europa para finales del Siglo XXI. Esa intensificación de las sequías se explica por el descenso de la precipitación, y especialmente por el incremento de la temperatura y ratio de evapotranspiración. En lo que refiere a los cambios de precipitación, en términos absolutos, la mayor reducción es proyectada en invierno. La expansión del cinturón de altas presiones subtropical es proyectada junto al desplazamiento de las tormentas hacia el norte de Europa, donde se proyectan condiciones más húmedas a finales del Siglo XXI. Este patrón de cambios esperados en Europa parece estar siendo observado durante las últimas décadas. Focalizando en la Península Ibérica, una mayor frecuencia e intensidad de los periodos de sequía desde 1980 corrobora la tendencia proyectada por simulaciones. No obstante, esa señal parece ser no tan robusta cuando se revisan periodos más largos de la Era Instrumental. Paralelamente, las proyecciones de precipitaciones continúan mostrando alta incertidumbre entre modelos y simulaciones de cada uno de ellos. Surge por tanto la necesidad de comprender óptimamente la variabilidad climática observada en el largo plazo, así como en qué factores radica la incertidumbre de las proyecciones climáticas. Bajo ese objetivo principal, esta tesis doctoral intenta aumentar el conocimiento sobre la variabilidad observada de la precipitación en Europa, fundamentalmente en la Península Ibérica, desde el origen de los registros disponibles. Conectando su comportamiento con la dinámica de los modos de variabilidad climática principales en la región, e.g., la Oscilación del Atlántico Norte (NAO). Para, entonces, evaluar si las proyecciones climáticas son capaces de interpretar toda la variabilidad climática que deriva en ciclos decadales y centenales de la precipitación. Los resultados confirman un comportamiento ciertamente singular en numerosos indicadores climáticos desde 1980. En la Península Ibérica, amplias regiones registran un descenso drástico de las precipitaciones, que se propaga, incluso con más intensidad, en las series hidrológicas. Esta tendencia es conectada principalmente con la intensificación de NAO hacia fases positivas, que se resume en una mayor frecuencia de altas presiones sobre las Azores. Al menos en la Era Industrial, nuestros resultados evidencian su comportamiento anómalo desde 1980 en base a varios indicadores como su rol más predominante, explicando más varianza que en décadas anteriores; siendo más intenso, algo sin precedentes; y mostrando un patrón espacial con ciertas particularidades. Aunque otros factores parecen jugar un papel importante, nuestros hallazgos muestran con alta confianza que el descenso de la precipitación invernal es el desencadenante principal de la intensificación de las sequías desde 1980 en la mayor parte del territorio de la Península Ibérica, y probablemente, en otras regiones del Mediterráneo Occidental. Dado que las proyecciones climáticas prevén la persistencia de la intensificación de NAO+ (e.g., expansión de la Célula de Hadley, intensificación del cinturón subtropical), estas condiciones más secas podrían extenderse durante las próximas décadas, e incluso agravarse, constituyendo una amenaza ambiental clave para la disponibilidad de recursos hídricos. No obstante, la magnitud de los cambios esperados difiere considerablemente entre modelos capaces de reproducir long-term variaciones en la circulación de larga escala, y aquellos modelos, demasiado rígidos, que no pueden. Esto abre un horizonte muy ilusionante en el que mejorar la habilidad de las simulaciones capturando completamente la variabilidad natural observada del sistema climático es una prioridad. Jamás podremos conocer con exactitud que depara al clima a escala regional, y sus impactos a los seres vivos en esos territorios, si los modelos climáticos continúan expresando cualquier sesgo intrínseco al capturar indicadores tan fundamentales como las condiciones sinópticas en el Atlántico Norte.The most advanced climate projections indicate, with high confidence, an increase in the frequency, persistence, and severity of dry periods in southern Europe by the end of the 21st century. This intensification of droughts is explained by a decrease in precipitation, and especially the rise temperatures and evapotranspiration rates. In terms of precipitation changes, the largest reduction is projected for winter. The expansion of the subtropical high-pressure belt is projected, along with the northward movement of storms into northern Europe, where wetter conditions are projected by the end of the 21st century. This pattern of expected changes in Europe appears to have been observed over the last few decades. Focusing on the Iberian Peninsula, a higher frequency and intensity of drought periods since 1980 corroborate the trend projected by simulations. However, this signal seems less robust when examining longer periods of the Instrumental Era. Additionally, precipitation projections continue to exhibit high uncertainty among models and their simulations. Therefore, there is a need to gain a comprehensive understanding of the long-term observed climatic variability, as well as the factors contributing to the uncertainty in climate projections. With this primary objective in mind, this doctoral thesis aims to enhance knowledge about observed precipitation variability in Europe, primarily in the Iberian Peninsula, from the beginning of available records. It seeks to connect this behavior with the dynamics of the major climate variability modes in the region, such as the North Atlantic Oscillation (NAO). The goal is to evaluate whether climate projections can effectively interpret all the climatic variability that results in decadal and centennial precipitation cycles. The results confirm a notably unique behavior in numerous climate indicators since 1980. In the Iberian Peninsula, extensive regions experience a significant decline in precipitation, which propagates, with even greater intensity, in hydrological series. This trend is primarily linked to the intensification of NAO into positive phases, resulting in a higher frequency of high-pressure systems over the Azores. At least during the Industrial Era, our results highlight its anomalous behavior since the 1980s based on several indicators, such as its more dominant role, explaining more variance than in previous decades, being more intense, something unprecedented, and showing a spatial pattern with certain particularities. Although other factors appear to play a significant role, our findings show with high confidence that the decrease in winter precipitation is the primary trigger for the intensification of droughts since 1980 in most of the territory of the Iberian Peninsula, and likely in other regions of the Western Mediterranean. Given that climate projections anticipate the persistence of NAO+ intensification (e.g., expansion of the Hadley Cell, intensification of the subtropical belt), these drier conditions could extend over the next decades, and even worsen, constituting a key environmental threat to water resource availability. However, the magnitude of the expected changes differs considerably between models capable of reproducing long-term variations in large-scale circulation and those models that are too rigid. This opens up an exciting horizon in which improving the ability of simulations to capture fully the observed natural variability of the climatic system is a priority. We will never be able to accurately predict what the climate holds at a regional scale, and its impacts on living beings in those territories, if climate models continue to exhibit inherent biases in capturing such fundamental indicators as synoptic conditions in the North Atlantic

Estudio del índice de aridez bajo escenarios de cambio climático en la cuenca del río Almanzora (Almería)

Ponencia presentada en: XI Congreso de la Asociación Española de Climatología celebrado en Cartagena entre el 17 y el 19 de octubre de 2018.[ES]El empleo de modelos climáticos regionales, concretamente de las proyecciones de precipitación y evapotranspiración de referencia (ET0) han servido para analizar los niveles de disponibilidad hídrica en escenarios de cambio climático en una cuenca de drenaje mediterránea con importantes transformaciones en la cobertura del suelo durante 1956-2007. A través del índice de aridez adoptado por la UNEP (1997) se han evaluado diferentes demandas de agua asociadas a los cambios experimentados en los usos del suelo. Los resultados muestran un descenso importante en la disponibilidad hídrica de la cuenca, especialmente en el escenario A2 (periodo 2071-2099). Este análisis espacial permite analizar las estimaciones en la evolución del cambio climático para diferentes coberturas del suelo, lo que puede ser de gran utilidad en la planificación y gestión del territorio de acuerdo a las recomendaciones IPCC para establecer políticas de mitigación y adaptación al calentamiento global.[EN]The use of the regional climate models, specifically the precipitation and evapotranspiration of reference (ET0) have been useful to analyse the levels of hydric availability at sceneries of climate change in a Mediterranean drainage basin with important changes in the land cover during 1956-2007. By using the aridity index taken by UNEP (1997), different demands of water related to the changes experimented in the land uses have been evaluated. The results show an important decline in the hydric availability of the basin, especially at A2 scenery (2071-2099 period). This spacial analysis enables to analyse the estimates in the evolution of the climate change for different ground covers, which can be very useful for the planning and territory management according to the IPCC recommendations to establish mitigation and adaptation to global warming policies

High resolution monitoring and probabilistic prediction of meteorological drought in a Mediterranean environment

Drought remains a costly natural disaster, with strong socio-economic and environmental impacts. Skilful seasonal drought forecasts can help to make early decisions. Here we assess the quality of a prototype seasonal forecasting system for a Mediterranean region (peninsular Spain + Balearic Islands) to predict meteorological drought as measured by the standardised precipitation index (SPI). We first show that there is a high agreement between the official data provided by the Spanish Meteorological Agency and the state-of-the art ERA5 reanalysis, building confidence in using these datasets. Thus, since the ERA5 data are provided in near-real time as it is updated on a monthly basis, it can be used to monitor drought evolution. Then, we demonstrate that it is possible to obtain skilful and reliable seasonal drought predictions several months in advance by applying an ensemble-based streamflow prediction system (ESP, an ensemble based on the rearrangement of historical data) using ERA5 data as initial conditions. The results indicate that a statistical persistence-based model could lead to an actionable seasonal drought forecasting skill thus providing the basis for a cheap and fast prototype for drought early warning

Evaluation of long-term changes in precipitation over Bolivia based on observations and Coupled Model Intercomparison Project models

Using observations and model simulations from the 5th and 6th phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively), this study evaluated changes in monthly, seasonal, and annual precipitation over Bolivia from 1950 to 2019. Results demonstrate that observed precipitation is characterized by strong interannual and decadal variability. However, long-term precipitation trends were not identified on the annual scale. Similarly, changes in seasonal precipitation were almost nonsignificant (p > .05) for the study period. Spatially, albeit with its complex orography, no substantial regional variations in observed precipitation trends can be identified across Bolivia. In contrast, long-term precipitation trends, based on CMIP5 and CMIP6 models, suggest a dominance of negative trends, mainly during austral winter (JJA) (−10%) and spring (SON) (−15%). These negative trends were more pronounced in the lowlands of Bolivia (−20%). Overall, these contradictory results highlight the need for validating precipitation trend outputs from model simulations, especially in areas of complex topography like Bolivia.This work was sup-ported by the research projects CGL2017-82216-R,PCI2019-103631, and PID2019-108589RA-I00, financedby the Spanish Ministry of Science and FEDER, theCROSSDRO project financed by the AXIS (Assessment ofCross(X)-sectorial climate impacts and pathways for Sus-tainable transformation), the JPI-Climate co-funded callof the European Commission, and the LINCGLOBAL-CSIC project (INCGLO0023, RED-CLIMA)