Self-similarity patterns of precipitation in the Iberian Peninsula

Summary An objective classification of the precipitation field over the Iberian Peninsula and the Balearic Islands is obtained. Data are derived from a high-resolution daily precipitation dataset obtained from in-situ measurements. The dataset, Iberian monthly Precipitation Dataset (IPD), consists of monthly precipitation data over a 25 km × 25 km grid from 1^st January 1961 to 31^st December 2003. Therefore, 960 data series over the Iberian Peninsula and the Balearic Islands are disposed over the grid for 43-year period. Multi-resolution wavelet analysis is used to extract similar information in the precipitation field at different timescales. An objective classification of the obtained wavelet coefficient series is carried out by means of the Kohonen’s neural network, also named Self-Organizing Map (SOM). SOM is formed by an unsupervised learning algorithm that may be used to find clusters of similar events in the input data and is able to identify some underlying dynamic structures of the multi-dimensional datasets. SOM is applied to the wavelet coefficients for intramonthly, intermonthly and interannual oscillations, obtaining self-organised maps which objectively identify similar zones of precipitation behaviour over the Iberian Peninsula. The homogeneity of the patterns is also studied by means of non-parametric correlations, energy scalograms and tests of significance. The intramonthly, intermonthly and interannual waves resulted in seven, five and three SOM patterns, respectively. As timescale increases, the wavelet series coefficients tend to be highly clustered. The results indicate that as the oscillation frequencies decrease, the Iberian precipitation behaves more linearly.     

Nocturnal offshore precipitation near the Mediterranean coast of the Iberian Peninsula

While nocturnal offshore precipitation, which produces rain cells and bands, has been studied in tropical areas, few studies have analyzed the occurrence of this phenomenon at higher latitudes. Using radar reflectivity, nocturnal rainfall in the western Mediterranean area has been detected near the coast of the Iberian Peninsula and North Africa. More than 50 events have been recorded since 2009. MM5 mesoscale simulations of some of the recorded events allow us to establish that the most likely causes for these precipitation events are: (1) the interaction between cold air masses conducted by drainage and katabatic winds, and (2) a wetter and warmer synoptic wind. Two different episodes are presented: one in the northeastern Iberian Peninsula, caused by stratiform clouds, which occurred at the mouths of three rivers; the other case, produced by convective clouds, occurred at the southern Iberian Peninsula and was caused by the drainage winds flowing down from some mountain ranges located close to the coast.     

Analysis of the precipitation and cloudiness associated with COLs occurrence in the Iberian Peninsula

Summary The Iberian Peninsula is one of the regions in the world with higher occurrence of cut-off low systems (COL). The aim of this paper is to analyse the weather events (rainfall and cloudiness layer) associated to COLs in the Iberian Peninsula with tools not previously used: (a) the use of the new multidecadal COLs database developed by Nieto et al (2005) that permit us to study a 41 years period (1958–1998), (b) the checking of the expected weather events (rainfall and cloudiness layer) associated with COLs in a conceptual model (Winkler et al, 2005) and (c) the extensive use of radiosoundings to analyse convective instability in areas inside and close to the COL. Two points of view are used to make the analysis: (1) a source oriented method, when a particular COL is followed and its associated precipitation and cloudiness is analysed over four quadrants in which Iberia was divided and (2) a receptor oriented method, when the precipitation associated to COLs is analysed in given areas, defined by patterns of precipitation. Results reveal that the precipitation and cloudiness patterns associated to COLs in the conceptual model reproduce quite well the main characteristics found over the Iberian Peninsula. The generalized idea that most of the COLs produce intense convective rainfall is show to be misleading. Convective phenomena are important usually when the centre of the COL is located on the Mediterranean region. Most of the rainfall associated with COLs comes from the baroclinic shield; specially in cases located over the west half of the Iberian Peninsula. It is shown that nearly 30% of COLs do not induce any rainfall; most of them located in the southern half of the Peninsula, and mainly during autumn. Only 30% of COLs produce generalized rainfall over the whole analysed territory, being most of them (about 90%) located over the western half of the Iberian Peninsula.     

Predictability of the spring rainfall in Northwestern Iberian Peninsula from sea surfaces temperature of ENSO areas

The influence of sea surface temperature (SST) of the ocean on seasonal rainfall in Northwestern Iberian Peninsula is studied for the period 1951–2006. Seasonal correlations were calculated for all seasons and different lags applied on SST. A test for field-significance considering the properties of finiteness and interdependence of the spatial grid was applied to avoid correlations by chance. The most significant and repetitive correlation is found between SST over Equatorial Pacific and spring rainfall. The correlation is maintained for different lags, and the common area that satisfies the criteria for statistical field significance is coincident with ENSO area. A forecast scheme is developed to predict spring rainfall anomalies based in SST over ENSO area in precedent seasons. An analysis of principal components was also carried out to obtain the main modes of the Pacific Ocean and their influence on spring rainfall in NWIP. This study concludes that for the period 1951–2006 the negative phase of ENSO, “La Niña”, almost always announces dry springs in NW Iberian Peninsula. However, the positive phase of ENSO, “El Niño”, does not anticipate the appearance of wet springs.     

Probable maximum precipitation for a 2-day duration over the Indian Peninsula

Summary For the purpose of providing information to hydrologists for designing costly and large hydraulic structures, estimates of probable maximum precipitation (PMP) for a 2-day duration for stations in the Indian Peninsula lying between 8° N to 20° N were calculated using the Hershfield statistical techniqe. Maximum annual 2-day rainfall data of 80 years from 1901 for 131 stations in the region were used. In order to obtain values of PMP, an enveloping frequency factor (k _m ) curve based on the actual rainfall data of stations in the region was developed. The enveloping curve was then utilised to estimate 2-day PMP values of all the 131 stations. Based on these PMP estimates, a generalised chart showing the spatial distribution of 2-day PMP was prepared. It was found that 2-day PMP estimates over the Indian peninsula varied from 40 to 95 cm and the average ratio of 2-day PMP to the highest observed 2-day rainfall was found to be 1.76.With 2 Figures     

Monthly precipitation mapping of the Iberian Peninsula using spatial interpolation tools implemented in a Geographic Information System

Summary In this study, spatial interpolation techniques have been applied to develop an objective climatic cartography of precipitation in the Iberian Peninsula (583,551 km²). The resulting maps have a 200 m spatial resolution and a monthly temporal resolution. Multiple regression, combined with a residual correction method, has been used to interpolate the observed data collected from the meteorological stations. This method is attractive as it takes into account geographic information (independent variables) to interpolate the climatic data (dependent variable). Several models have been developed using different independent variables, applying several interpolation techniques and grouping the observed data into different subsets (drainage basin models) or into a single set (global model). Each map is provided with its associated accuracy, which is obtained through a simple regression between independent observed data and predicted values. This validation has shown that the most accurate results are obtained when using the global model with multiple regression mixed with the splines interpolation of the residuals. In this optimum case, the average R ² (mean of all the months) is 0.85. The entire process has been implemented in a GIS (Geographic Information System) which has greatly facilitated the filtering, querying, mapping and distributing of the final cartography.     

Extreme maximum temperature events and their relationships with large-scale modes: potential hazard on the Iberian Peninsula

Theoretical and Applied Climatology - The aim of this paper is to analyze spatiotemporal distribution of maximum temperatures in the Iberian Peninsula (IP) by using various extreme maximum...     

Drought variability and change across the Iberian Peninsula

As a pivotal section of the Silk Road in northwest China, the Hexi Corridor is a popular tourist destination. In this study, the tourism climate conditions in this region were discussed using the Physiologically Equivalent Temperature (PET) and the Climate-Tourism/Transfer-information-Scheme (CTIS) from 1980 to 2012. Overall, cold or cool stress was prevalent in the area, and the optimal travel period was from May to September. With global warming, the annual numbers of cumulative days with relatively cold conditions decreased, and the annual numbers of cumulative days with comfortable and relatively hot conditions increased. Two typical stations, Wushaoling and Dunhuang, were compared and analysed for their tourism climate information according to the frequency of PET and CTIS conditions, respectively. In addition, regional variations in the tourism climate conditions based on geographic information systems (GIS) were investigated during the optimal travel period.     

Multi-day rainfall trends over the Iberian Peninsula

In order to analyze the effects of the duration of precipitation events, trends in extreme rainfall over the Iberian Peninsula (IP) for multi-day extreme precipitation events (1 to 7?days) were evaluated from records of 52 observatories regularly distributed over Iberia with no missing data for the common period 1958–2004. Two approaches were used: first, the nonparametric Mann–Kendall test together with the Sen method, and second, a parametric test based on the statistical theory of extreme values, involving time-dependent parameters to account for possible temporal changes in the frequency distribution. It was found that, in winter, there were significant negative trends for a great part of the Iberian Peninsula, but significant positive trends for the southeast over areas that shrank as the number of days considered for the precipitation event increased. Spring also showed negative trends for a great part of the IP but with a major area of positive trend over the northeast that remained unchanged when considering the maxima of from 1 to 7?days of rainfall. Autumn showed a bipolar spatial pattern, with the west being positive and the east negative.     

Analysis of UVB values in the centre of the Iberian Peninsula

Records of UV data started in Madrid at the beginning of the 90's decade. After some quality control on the data a seven year period from 1996 to 2002 was selected to perform an analysis of daily and seasonal variability of solar ultraviolet B (UVB) values at the centre of the Iberian Peninsula. Instruments used are a Brewer MKIV spectrophotometer and a YES UVB-1 broadband pyranometer. Both instruments provided integrated daily values according with the Diffey spectrum although they have different measurement procedures. Data statistics from each instrument for the same period and statistical relationships between daily values from both instruments are shown. As broadband YES provided a record with fewer time gaps, analysis of UVI extreme values is performed using that instrument. The relationship between UVB values with ozone, cloudiness and visible radiation has been described in several papers for different places in the world. In this paper, those relationships are shown for Madrid. A discussion about specific problems found when trying to isolate every effective factor is also included. Some of those relationships could be helpful to retrieve UVB values from other ancillary data as visible radiation and cloudiness. Finally, a detailed study for 10 days in June 1997 when the maximum record of daily values from the present time series was obtained, highlight the close correlation between total ozone content and the daily variability of UVB for similar amounts of incoming radiation.     

Moisture recycling over the Mackenzie basin

Abstract

Moisture recycling over the Mackenzie basin is investigated by estimating the precipitation recycling ratio (the ratio of precipitation derived from local evaporation to the total precipitation within the basin) for the region with the National Centers for Environmental Prediction (NCEP) reanalysis dataset and the Meteorological Service of Canada (MSC) precipitation climatology. The results suggest that recycling is very active over the region during the warm season (April – August) and extremely inactive during the cold season. The annual recycling ratio estimated for the basin is about 0.25, which is close to that estimated by others for the Mississippi and Amazon basins despite the lower annual evapotranspiration over the Mackenzie basin.

The high recycling ratios and the recycling patterns estimated for the basin during the warm season are found to be consequences of the unique topographical and climatic settings characterizing the region. Analysis of conditions during the years having anomalous spring and summer precipitation suggests that the large‐scale atmospheric setting could act in concert with the basin's unique topographic and surface characteristics to increase or to decrease precipitation and its recycling over the basin, depending on whether the basin is under the influence of a persistent large‐scale low or a high pressure system. In the former case, much of the recycled precipitation would fall over the north‐western parts of the basin where the runoff ratios are relatively high, and thus enhance the summer discharge from the basin. When the basin is under the influence of a persistent high pressure system, much of the recycled precipitation would fall over the southern part of the basin where the runoff ratios are relatively low, and thus reduce the discharge from the basin. It is suggested that this latter effect might have contributed to the record low summer discharge from the basin during 1995.     

Characteristics of the precipitation recycling ratio and its relationship with regional precipitation in China

A dynamic recycling model (DRM) with an analytical moisture trajectory tracking method, together with Japan Meteorological Agency 25-year reanalysis data, is used to study the regional precipitation recycling process across China, by calculating the regional recycling ratio (ρ _r ) at the daily time scale during 1979–2010. The distribution of ρ _r shows that, in western China, especially the Tibetan Plateau and its surrounding areas, precipitation is strongly dependent on the recycling process associated with regional evaporation. In Southeast China, however, the contribution from the recycling processes is much smaller due to the influence of the summer monsoon. A precipitation threshold value of about 4 mm/day is obtained from detailed analysis of both extreme and all-range ρ _r years. According to this threshold, China is classified into three types of sub-regions: low-precipitation sub-regions (mainly in the northwest), high-precipitation sub-regions (mainly in the south), and medium-precipitation sub-regions (mainly in the northeast). It is found that ρ _r correlates positively with precipitation, as well as convective precipitation (P _CP) and large-scale precipitation (P _LP) in the low-precipitation sub-regions. However, negative ρ _r ?～?P _LP correlations are found in the high-precipitation sub-regions and nonsignificant correlations exist in the medium-precipitation sub-regions. As P _CP is mainly locally generated due to mid-latitude mesoscale systems and the cumulus parameterization used in producing the reanalysis, the recycling ratio positively correlates to the ratio P _CP/P _LP in almost all sub-regions, particularly in the Tibetan Plateau and its surrounding areas. The correlation between radiation flux and ρ _r suggests more net radiation supports more evaporation and higher ρ _r , especially in the high-precipitation sub-regions. The influence of clouds on shortwave radiation is crucial, since evaporation is suppressed when the amount of cloudiness increases, especially in the high-precipitation sub-regions. Together with the consideration of soil moisture, it can be inferred that limited soil moisture inhibits evaporation in the low-precipitation sub-regions, while the energy or radiation is the dominant factor controlling evaporation in the high-precipitation sub-regions.     

Physically based evaluation of climate models over the Iberian Peninsula

A novel approach is proposed for evaluating regional climate models based on the comparison of empirical relationships among model outcome variables. The approach is actually a quantitative adaptation of the method for evaluating global climate models proposed by Betts (Bull Am Meteorol Soc 85:1673–1688, 2004). Three selected relationships among different magnitudes involved in water and energy land surface budgets are firstly established using daily re-analysis data. The selected relationships are obtained for an area encompassing two river basins in the southern Iberian Peninsula corresponding to 2 months, representative of dry and wet seasons. The same corresponding relations are also computed for each of the thirteen regional simulations of the ENSEMBLES project over the same area. The usage of a metric based on the Hellinger coefficient allows a quantitative estimation of how well models are performing in simulating the relations among surface magnitudes. Finally, a series of six rankings of the thirteen regional climate models participating in the ENSEMBLES project is obtained based on their ability to simulate such surface processes.     

Sensitivity of the Iberian Peninsula climate to a land degradation

Two six-year simulations, a land degradation scenario and a control, were performed by applying a regional climate model nested in ECMWF analyzed data to the Iberian Peninsula. The simulated time period (1993-98) includes extremely anomalous dry and rainy years. The land degradation scenario assumed a decrease in vegetation cover and an alteration of the soil properties resulting from future increases of greenhouse gases and human activity. Simulation results show that the impact of land degradation on the climate of the Iberian Peninsula depends on local factors (the intensity of degradation and geographical location) but some noticeable non-local effects are also present. Local factors result in an increase of the surface temperature which is almost linearly related to the degradation intensity. A stronger decrease in precipitation is observed in the less degraded regions, indicating that non-local effects are more relevant to changes in precipitation. The highest sensitivity to land degradation is observed in the summer season, consisting of an increase in 2 m temperature and a reduction in precipitation. In winter, the rainiest season on the Iberian Peninsula, the impact of land degradation on precipitation is almost negligible.     

Evolution of annual rainfall irregularity in the southwest of the Iberian Peninsula

The areas of the Iberian Peninsula with Mediterranean climate are characterised by rainfall irregularity. Standard statistical estimation methods provide a limited insight of all the dimensions of such irregularity. Based on different techniques to describe the inter-annual irregularity of rainfall, the authors develop a new method: the disparity indices. These indices are then applied to several historical rainfall series (dating from the end of the nineteenth century up to the present) from the southwest of the Iberian Peninsula. Similar rainfall irregularity patterns are found in all weather stations in the studied area, confirming their belonging to the same climatic region. The results indicate a relative stability during the first third of the twentieth century, coinciding with a period of low precipitation and a progressive increase during the last three decades. The use of a new index named specific disparity index has proven be useful in highlighting the irregularity within the rainfall series at each meteorological station. This new index could contribute to monitor future changes in precipitation within the general framework of research on climate change. Although Mediterranean ecosystems are adapted to important fluctuations in the rainfall regime, this increase in irregularity may affect rivers, wetlands and the hygrophytic vegetation.     

A spectral analysis of Iberian Peninsula monthly rainfall

Summary A spectral analysis of Iberian Peninsula monthly rainfall series was carried out. The data set consists of monthly precipitation records from 40 meteorological observatories over 74 years (1919–1992). The stations are representative of most of the Iberian Peninsula. The rainfall series were analyzed spatially by means of Principal Component Analysis (PCA) and temporally by means of the Multi-Taper Method (MTM) of spectral analysis of by Monte-Carlo Singular Spectrum Analysis (MCSSA). The PCA gave six dominant modes of variation which explain 75% of the variance with each component affecting a different region of the Peninsula. The spectral analysis showed 7 year oscillations for the dominant pattern and 2.7 and 16 years for the third pattern. The 7-year oscillation seems to be related to other climatic oscillations recorded in the northern hemisphere while the 2.7-year oscillation could be related to the ENSO phenomenon. Received July 18, 2000 Revised April 19, 2001     

Validation of IPCC AR4 models over the Iberian Peninsula

This paper reports analysis of the ability of 24 coupled global climate models that were used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change to simulate the current monthly seasonal cycle of sea level pressure, surface air temperature and precipitation over the Iberian Peninsula in the last two decades of the twentieth century. The period investigated runs from 1979 to 1998. In order to assess the performance of the models, averaged seasonal cycles and probability density functions (PDFs) calculated from model simulations are compared with the corresponding seasonal cycles, whilst PDFs are also obtained using the data from the ERA40 reanalysis and the Global Precipitation Climatology Project. We found that simulated PDFs generally provided a better fit to actual PDFs than seasonal cycles do. This conclusion indicates that when evaluating model performance, the climate variability as measured by means of PDFs is not the only climatic element that should be tested. Regarding the comparison based on the seasonal cycle, results also show that the root mean square skill score is more useful than the r skill score. To rank the AR4 models, sea level pressure, surface air temperature and precipitation variables were selected and a group of five AR4 models were identified as the models which best reproduce current climate in the area: MIROC3.2-HIRES, MPI-ECHAM5, GFDL-CM2.1, BCCR-BCM2.0 and UKMO-HADGEM1. The rank obtained should not be understood in a hierarchical manner because there is a certain degree of internal variability in the model ensembles. Finally, it should be noted that these results are in good agreement with other classifications found in the scientific literature.     

Climate-induced changes in river water temperature in North Iberian Peninsula

With the surface air temperature (SAT) data at 37 stations on Central Yunnan Plateau (CYP) for 1961–2010 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, the temporal-spatial patterns of the SAT trends are detected using Sen’s Nonparametric Estimator of Slope approach and MK test, and the impact of urbanization on surface warming is analyzed by comparing the differences between the air temperature change trends of urban stations and their corresponding rural stations. Results indicated that annual mean air temperature showed a significant warming trend, which is equivalent to a rate of 0.17 °C/decade during the past 50 years. Seasonal mean air temperature presents a rising trend, and the trend was more significant in winter (0.31 °C/decade) than in other seasons. Annual/seasonal mean air temperature tends to increase in most areas, and higher warming trend appeared in urban areas, notably in Kunming city. The regional mean air temperature series was significantly impacted by urban warming, and the urbanization-induced warming contributed to approximately 32.3–62.9 % of the total regional warming during the past 50 years. Meantime, the urbanization-induced warming trend in winter and spring was more significant than that in summer and autumn. Since 1985, the urban heat island (UHI) intensity has gradually increased. And the urban temperatures always rise faster than rural temperatures on the CYP.     

Effect of spring soil moisture over the Indo-China Peninsula on the following summer extreme precipitation events over the Yangtze River basin

Climate Dynamics - Extreme precipitation events (EPEs) over the Yangtze River basin (YRB) exert widespread impacts on regional ecological environment and people’s life. Using observed...