HS7.10 | Trends and Variations in Hydroclimatic Variables: Links to Climate Variability and Change
EDI
Trends and Variations in Hydroclimatic Variables: Links to Climate Variability and Change
Convener: Priyank Sharma | Co-conveners: Ramesh Teegavarapu, Achala Singh
Orals
| Tue, 25 Apr, 16:15–18:00 (CEST)
 
Room 2.31
Posters on site
| Attendance Tue, 25 Apr, 10:45–12:30 (CEST)
 
Hall A
Posters virtual
| Attendance Tue, 25 Apr, 10:45–12:30 (CEST)
 
vHall HS
Orals |
Tue, 16:15
Tue, 10:45
Tue, 10:45
A persistent rise in the mean global temperatures is observed due to the continuous accumulation of greenhouse gases within the atmospheric system. Global warming has resulted in climate change, manifesting changes in the hydrological cycle through long-term changes in temperature and precipitation patterns at different spatial and temporal scales. Thus, investigating trends and variability in climate extremes would help us quantify the regional climate change impacts. Moreover, stationarity assessment is essential for hydrologic design, particularly in a changing climate. In addition, the climate variability influences through large-scale oceanic-atmospheric circulations modulate the hydroclimatic means and extremes. Thus, it is inevitable to statistically analyze the long-term changes in hydroclimatic variables and explore their linkages to climate change and variability.

This session focuses on the application of statistical techniques for objectively assessing trends in hydroclimatic variables at different temporal, regional, and continental scales to assess any discernible links to climate variability and change. In addition, this session aims to explore the applicability of emerging techniques and approaches for detecting stationarity in hydroclimatic time series. This session will also invite submissions that develop and apply new indices for understanding regional hydroclimatological variability to aid water resources management. Research studies unravelling the climate variability effects on the hydroclimatic conditions at local and global scales will be appreciated. Further, research studies assessing the co-evolution of hydroclimatic variables under the influence of climate variability and change will also be welcomed.

Orals: Tue, 25 Apr | Room 2.31

Chairpersons: Priyank Sharma, Ramesh Teegavarapu
16:15–16:20
16:20–16:30
|
EGU23-511
|
ECS
|
On-site presentation
Matheus Henrique Tavares, Maria Angélica Cardoso, David Motta-Marques, and Carlos Ruberto Fragoso Jr

Climate change impacts on lake surface water temperature (LSWT) have been mostly investigated in deep northern lakes, and are less understood in southern hemisphere shallow lakes. We evaluated the seasonal warming rates of a large (surface area c.a. 10000 km²) shallow choked lagoon in southern Brazil, with a 22 yr time series of MODIS-derived LSWT, and meteorological data. We found high LSWT warming, with a rate of 0.6°C dec-1 in spring and of 0.3°C dec-1 in summer. We also found a high correlation between water and mean air temperature trends, as well as a substantial shortening of the cold season. Spatially, there was some homogeneity in the warming rates but prominent point spatial differences, which may result from the variability of the tributaries’ temperature or discharge or decreased water transparency. The high warming rates found here are comparable to those found in deep northern lakes although the changes and processes of heating differ. The stronger warming in early spring can result in accelerated process rates and an earlier start of the phytoplankton growing season.

How to cite: Tavares, M. H., Cardoso, M. A., Motta-Marques, D., and Fragoso Jr, C. R.: Warming rates in a large subtropical shallow Brazilian lagoon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-511, https://doi.org/10.5194/egusphere-egu23-511, 2023.

16:30–16:40
|
EGU23-453
|
ECS
|
Virtual presentation
Jaya Bhatt, Vemavarapu Venkata Srinivas, Vemavarapu Venkata Srinivas, and Vemavarapu Venkata Srinivas

Design and risk assessment of large hydraulic structures, whose failure can cause catastrophic damage to the environment, ecology, life and property, are based on Probable Maximum Precipitation (PMP). It is deemed as the theoretical upper bound of the maximum precipitation that is physically possible over a given area for a specified duration. The conventional approaches for estimating PMP are based on stationarity assumption, i.e., the current climatic conditions will remain unchanged even in the future. But the recent increase in extreme precipitation events across the globe and projected increase in the same for future climatic scenarios raises questions on the validity of the stationarity assumption. This issue has gained attention in recent years, and efforts have been directed towards improving existing approaches and devising novel methodologies that would yield reliable PMP estimates in changing climatic conditions. Several researchers have proposed different variations of the widely used storm maximization method to account for non-stationarities arising due to changing climate. The variations imbibe the potential change in PMP resulting either from the trend in precipitable water or from the complex interaction of drivers of PMP. There is a need to compare their relative performance to quantify if the improvement offered by complex variants is significant compared to simple variants in different parts of the globe. In this study, it is investigated through a case study on the frequent flood-prone Mahanadi River Basin in India. For this analysis, future projections of various atmospheric variables (e.g., precipitation, dew point temperature, precipitable water) were obtained from 5 GCMs (General Circulation Models) corresponding to two CMIP6 SSP (Coupled Model Intercomparison Project-6 Shared Socioeconomic Pathways) forcing scenarios namely, SSP1-2.6 and SSP5-8.5. The PMP estimates obtained from improved variants were also compared with their conventional stationary counterpart to assess the effect of dispensing the stationarity assumption.

How to cite: Bhatt, J., Srinivas, V. V., Srinivas, V. V., and Srinivas, V. V.: Comparison of different variants of storm maximization method for Probable Maximum Precipitation estimation in changing climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-453, https://doi.org/10.5194/egusphere-egu23-453, 2023.

16:40–16:50
|
EGU23-2305
|
ECS
|
Virtual presentation
Tapobeeva Sahoo, Vijaykumar Bejagam, and Ashutosh Sharma

Extreme events are becoming more frequent, intense, and prolonged, with significant impacts on human lives, the environment, and regional development. Rising temperature due to global warming is one the crucial factors causing the rise in the frequency and severity of extreme events. The worst extreme events are caused by a combination of more than one factor/variable, which makes it essential to study the co-occurrences of extremes, also known as compound extremes. In the present study, four compound extremes are assessed over India for the time period of 1971-2020 using two different statistical approaches, empirical approach, and multivariate distribution analysis. The variables used are temperature and precipitation, having a resolution of 0.25° × 0.25°. Firstly, the empirical analysis of four compound extremes, Hot-Dry, Hold-Wet, Cold-Dry, and Cold-Wet, is done by providing threshold percentiles (25th and 75th) to count the exceedance, and Mann Kendall's trend, p-value, and Sen's slope are calculated to assess the changes and significance of the extremes. Next, multivariate distribution analysis using Copula is conducted to study the dependency between temperature and precipitation. The results indicate a significant increase in compound Hot-Dry and Hot-Wet extremes across the country, with a decrease in Cold-Dry and Cold-Wet conditions. The changes in extremes are more pronounced in the later period (1996-2020) than in the earlier period (1971-1995). This study provides insight into the evaluation of compound extremes in India over the past 50 years, which can help us understand the changes and frequency of their occurrence.

How to cite: Sahoo, T., Bejagam, V., and Sharma, A.: Assessment of compound extremes using statistical methods in India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2305, https://doi.org/10.5194/egusphere-egu23-2305, 2023.

16:50–17:00
|
EGU23-12596
|
ECS
|
Highlight
|
On-site presentation
Sofia Nerantzaki, Simon Michael Papalexiou, ‪Chandra Rupa Rajulapati, and Martyn Clark

Annual Maxima (AM) and Peaks over Threshold (POT) are the two most common approaches to define extreme time series in hydroclimatic variables. Both methods present limitations. AM frequently fails to include significant extremes that occur during the same year. Conversely, POT may only include clustered values from a few years thus excluding many years from the analysis, especially when the threshold is set high. Additionally, a big challenge in POT is identifying the threshold which can markedly affect the results.

Here, we merge notions from both AM and POT, preserving the strengths of each approach, to extract extreme temperature series and estimate the trends in their frequency and magnitude. We select the values larger than or equal to the minimum of the AM series as high temperatures (HT) (lower than or equal to the maximum of the Annual Minima as the low temperatures – LT). Thus, each year of the HT, LT series has at least one extreme value (H1, L1). We apply the method to 4797 quality-controlled raw station observations from a global dataset of maximum and minimum temperatures over 1970-2019 when warming accelerates. To examine changes in H1-L1 frequency and magnitude, we estimate the ratio of observed to expected H1 (L1) annual occurrences, and the difference between the observed and expected mean H1 (L1) annual temperature values, respectively. We estimate the regression slopes of these ratios at the station level, regionally in 2°×2° grids, and globally. We then compare these trends with the ones obtained from AM and POT series. The proposed method adapts the threshold for each sample, and finds a compromise among all tested methods, thus being a flexible approach that can be applied to any non-intermittent variable.

 

Acknowledgment

This research was supported by a GWF Ph.D. Excellence Scholarship from the Global Institute for Water Security (GIWS), University of Saskatchewan

How to cite: Nerantzaki, S., Papalexiou, S. M., Rajulapati, ‪. R., and Clark, M.: Estimation of global extreme temperature trends by merging Annual Maxima and Peaks Over Threshold, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12596, https://doi.org/10.5194/egusphere-egu23-12596, 2023.

17:00–17:10
|
EGU23-6544
|
ECS
|
Virtual presentation
Rahul Sheoran and Umesh C. Dumka

In combination with Sen's slope, the non-parametric Mann–Kendall (MK) test is one of the most often used statistical techniques for determining a time series' trends. A serially uncorrelated time series is required for the MK test since the autocorrelation in the dataset seriously affects the type 1 and type 2 errors and reduces the performance of the MK test in detecting the statically significant trend. To mitigate this problem, numerous prewhitening techniques (PW, PW-Cor, TFPW-Y, TFPW-WS, VCTFPW; See Collaud Coen et al., 2020) have been developed that effectively reduce lag-1 autocorrelation. In this work, we have proposed a new prewhitening scheme (named as TFPW-Mod) and compared it with previous prewhitening schemes by constructing 5000 linear-trend superimposed (β) AR1 time series with lag-1 autocorrelation (ρ1) using Monte Carlo simulation. We found that the new prewhitening approach keeps a very good balance between maintaining a low number of type 1 and type 2 errors. The results show that the occurrence of both types of errors largely depends on the length of the time series, with longer periods leading to a strong reduction of errors and to lower bias in the trend slope estimation. For weaker trends and/or the low number of samples, TFPW-Mod couldn’t restore the power of test. However, for a strong trend, this method yields the strongest power, almost independent of the lag-1 autocorrelation. The slope estimation of TFPW-Mod is robust for lower/Medium ρ1, but significantly deviates from the original trend for highly correlated time series. In most cases, βTFPW-Mod has lower RMSEs than βVCTFPW, and leads to the unbiased slope estimation with better accuracy.

How to cite: Sheoran, R. and Dumka, U. C.: A new prewhitening approach for trend analysis in the autocorrelated time series., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6544, https://doi.org/10.5194/egusphere-egu23-6544, 2023.

17:10–17:20
|
EGU23-10305
|
ECS
|
Virtual presentation
Vlad-Alexandru Amihăesei, Dana Magdalena Micu, Alexandru Dumitrescu, Sorin Cheval, Marius-Victor Bîrsan, and Lucian Sfîcă

In the regions with temperate climate, solid precipitation usually prevails during the winter time. However, a warming climate could alter the timing of snow accumulation and resulted amounts with major impact on the hydrological cycle. This study analyses the changes in the monthly snow-to-liquid precipitation ratio (SLPR)  over the October-May interval in Romania, based on daily precipitation, air temperature and snow depth data provided by 114 weather stations from the national meteorological monitoring network, over the 1961-2021 period. The observed trends showed a country-wide and significant decline in SLPR. The most notable decline is observed during the late winter and early spring months (February-March), with decreasing trends at over 70% of the weather stations, although only 20% suggest statistically significant changes (p value < 0.05). The autumn months (October and November) depict no statistically trends. The trends observed in the late spring (April and May), show a strong decline in SLPR for most mountain weather stations (above 1,000 m), at rates that could exceed 5% per decade (e.g., Tarcu weather station, 2,200 m, the Southern Carpathians). Evidence of elevation dependency of SLPR trends has been found in spring. The results show that the SLPR declines with altitude, especially in April (R2 = .30) and May (R2 = .67), when the correlations are statistically significant (p<0.05).

This work was co-funded by the European Social Fund, through Operational Programme Human Capital 2014-2020, project number POCU/993/6/13/153322, project title  “Educational and training support for PhD students and young researchers in preparation for insertion into the labor market”.

 

 

 

How to cite: Amihăesei, V.-A., Micu, D. M., Dumitrescu, A., Cheval, S., Bîrsan, M.-V., and Sfîcă, L.: Observed trends in the snow-to-liquid precipitation ratio over Romania, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10305, https://doi.org/10.5194/egusphere-egu23-10305, 2023.

17:20–17:30
|
EGU23-8992
|
ECS
|
On-site presentation
Hadir Abdelmoneim, Sameh A. Kantoush, Mohamed Saber, Hossam M. Moghazy, and Tetsuya Sumi

Natural disasters like droughts and flood events have frequently been occurring due to climate change in the global pattern of precipitation in recent decades. Estimating the future spatiotemporal precipitation variability is necessary to mitigate climate change's impact, particularly extreme precipitation events. However, global and regional climate models typically vary on the projected change in precipitation characteristics over particular regions. Therefore, this study comprehensively evaluates historical and future climate models in terms of spatial distribution, annual cycles, and frequency distributions of precipitation over the Blue Nile basin (BNB) based on different statistical indices. Also, the autocorrelated time series data were subjected to the Mann-Kendall (MK) and Sen's slope estimator tests to identify trends. Many regional and global climate models, such as HadCM3, ECHAM5, MPI-ESM-LR, and EC-EARTH, are employed not only better to understand the discrepancy and the uncertainties of climate models but also to estimate the impact of climate change in the extreme precipitation events over the Blue Nile basin (BNB). Overall, our finding would serve as a benchmark for flood risk mitigation research and water resources management applications over the Blue River basin.

How to cite: Abdelmoneim, H., Kantoush, S. A., Saber, M., Moghazy, H. M., and Sumi, T.: Exploring and investigating the performance of the global and regional climate models in precipitation over The Nile River basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8992, https://doi.org/10.5194/egusphere-egu23-8992, 2023.

17:30–17:40
|
EGU23-10952
|
ECS
|
Virtual presentation
Siddik Barbhuiya, Meenu Ramadas, Suraj Jena, and Shanti Biswal

In order to effectively plan, design, and manage water resources, it is necessary to understand the trends present in hydro-climatic variables such as streamflow and rainfall. In this study we used the Pettitt’s test as well as the standard normal homogeneity test (SNHT) to discover the trends in streamflow in the Upper Narmada Basin during the 1990 to 2018 period. The Upper Narmada basin extends over an area of 45, 580 square kilometers lies between latitudes 21°20’ N and 23°45' N and longitudes 72°32' E and 81°45’ E in India. From the flow records from gauges in this study basin, change points in the flow regime are thus identified.

Additionally, we performed Mann–Kendall (MK) test, modified Mann–Kendall (MMK) test, Sen's slope (SS) analysis to quantify the trends in streamflow time series. While the MK and MMK tests determine whether a trend is monotonically increasing or decreasing over time, SS suggests the rate of temporal change of streamflow variable. Further, we used advanced machine learning algorithms such as random forest (RF) and long short-term memory (LSTM) to develop flow forecasting models for few gauging sites in the study basin. In this way it is possible to address gaps in the flow records and perform long term analysis of gauge data.

Keywords: Trend analysis, Change point detection, Machine Learning Algorithm, LSTM, Upper Narmada Basin

 

 

 

How to cite: Barbhuiya, S., Ramadas, M., Jena, S., and Biswal, S.: Trend Analysis and Forecasting of Streamflow in the Upper Narmada Basin using Random Forest (RF) and Long Short-Term Memory (LSTM) Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10952, https://doi.org/10.5194/egusphere-egu23-10952, 2023.

17:40–17:50
|
EGU23-11523
|
ECS
|
Virtual presentation
Swagatika Chakra, Harsh Oza, Akash Ganguly, Virendra Padhya, Amit Pendey, and Rajendra Dattatray Deshpande

The global hydrological cycle is changing in response to climate change and anthropogenic influence. The rainfall, on an annual or sub-decadal timescale, has exhibited erratic and substantial deviation from the long-term average in different parts of the world. Consequently, there are epochs of higher or lower than average rainfall but these are missed in long-term monotonic trend.

As commonly experienced, the rainfall within different geographical regions also varies significantly in terms of magnitude and timing, and on a smaller spatial scale. Integrating large geographical areas and long timescales for monotonic rainfall trend analyses for the meteorologically homogenous regions provides a general picture which is useful for the purpose of administration, water management and distribution. However, it cannot discern the decadal to multi-decadal rainfall variation in different parts of a meteorologically homogenous region and hence a more advanced and comprehensive approach is required for advancing scientific understanding about the hydrometeorological processes and factors governing multi-decadal rainfall variation.

In this study, an innovative approach is presented which involves: (1) 31 years moving average of percentage departure of seasonal rainfall for 120 years at district level; (2) 15 year sliding slope analyses to identify the year of inflection point based on change in direction of slope; (3) K-Means cluster analyses; (4) normality test of clusters based on Z score; and determination of timeframe during which rainfall trend changed significantly.

This approach was tested in the North East India where the rainfall is derived by one of the most dynamic and complicated meteorological systems. Improving understanding about rainfall variability in Northeast India is also very important from ecological, environmental and strategic point of views. Using the above approach, long-term rainfall data (1901-2020) has been analyzed at a district level in Northeast India. Using K means clustering method time windows of prominent change in rainfall trend have been identified. It is inferred from this study that Northeast India has experienced three major climatological events, during 1929-1941, 1961-1971, and 1984-1992. The first and the third events involving a trend reversal from increasing to decreasing nature around 1929-1941 and 1984-1992 affected respectively 49% and 43% area of Northeast India. The second event involving a trend reversal from decreasing to an increasing trend around 1961-1971 impacted 38% of northeastern India.

The meteorological processes corresponding to these timeframes, which could have caused these major rainfall trend reversals are being examined.

How to cite: Chakra, S., Oza, H., Ganguly, A., Padhya, V., Pendey, A., and Deshpande, R. D.: An innovative approach to discern variation in long-term regional monsoonal rainfall trend in North Eastern India., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11523, https://doi.org/10.5194/egusphere-egu23-11523, 2023.

17:50–18:00
|
EGU23-10274
|
On-site presentation
Jinhui Jeanne Huang

Both climate change and intensified urban development will affect the temporal and spatial distribution of rainfall. There is still a lack of relatively quantitative and comparative studies. Most cities in China entered the rapid urbanization stage around 2000. This study focuses on the megacities Beijing, Shenzhen and Hong Kong. Based on rainfall observation data and land use and other remote sensing image data, this study investigates the impacts of the impervious areas on the temporal and spatial changes of short-duration and long-duration heavy rainfall before and after rapid urbanization. The impact of climate change on rainfall intensity is also analyzed. The results show that there are huge spatial shifts in rainfall after rapid urbanization. For example, it is observed that the center of the heavy rainfall shifts from northeast to southwest, and the hydrological homogenous areas in Beijing have increased from two to three after rapid urbanization. Meanwhile, with the influence of climate change, the intensity of rainfall is increasing, but due to urbanization, the increase varies greatly in each hydrological homogenous area. Shenzhen and Hongkong, the neighbor cities without physical boundaries, have entered into different urbanization stages since 1990. Hong Kong has developed very slowly, while Shenzhen has developed very rapidly. As a result, the short-duration heavy rainfall is mainly concentrated in Shenzhen, and the long-duration heavy rainfall is mainly concentrated in Hongkong. The short-duration heavy rainfall in Shenzhen mostly occurs at noon, while that in Hong Kong mostly occurs in the morning. The urbanizations of Hong Kong and Shenzhen are different, which resulted in different impacts on rainfall in these two cities. This study examines the impact mechanisms of urbanization and climate change on rainfall in cities in different climate zones. It provides scientific basis in supporting the city planning and the development of resilient cities.

How to cite: Huang, J. J.: The study of the changes in precipitation induced by intensified urbanization and climate change by observational records, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10274, https://doi.org/10.5194/egusphere-egu23-10274, 2023.

Posters on site: Tue, 25 Apr, 10:45–12:30 | Hall A

Chairpersons: Ramesh Teegavarapu, Priyank Sharma
A.139
|
EGU23-3525
|
Highlight
Ruud van der Ent, Maarten Doekhie, Mees Fokkema, Wenyu Zhou, Nick van de Giesen, and Gaby Gründemann

In a recent analysis of 25 CMIP6 models, Gründemann et al. (2022, https://doi.org/10.1038/s43247-022-00558-8) have shown that by the end of this century, daily land rainfall extremes could increase in magnitude between 10.5% and 28.2% for annual events (1 year return period), and between 13.5% and 38.3% for centennial events (100 year return period). The higher relative increase for larger return period was consistent for all climate models and scenarios. However, this study was solely based on model output and so far, this finding was not validated by observations. Using a large sample of stations with long time series, we analyzed whether the rare extremes have indeed been increasing relatively more because of global warming. Moreover, we analyzed sensitivity to the choice of time period, return period and rainfall duration.

How to cite: van der Ent, R., Doekhie, M., Fokkema, M., Zhou, W., van de Giesen, N., and Gründemann, G.: Do observations show that rare extremes increase relatively more compared to common extremes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3525, https://doi.org/10.5194/egusphere-egu23-3525, 2023.

A.140
|
EGU23-5363
Priya Shejule and Dr. Sreeja Pekkat

Identification and precise quantification of rainfall trend are crucial for researchers to understand the variations in rainfall over a longer period of time. On a global scale, climate change is influencing the intensity and frequency of rainfall, leading to extreme rainfall events. The expeditious and systematic consideration of rainfall changes is important in this context. In the given study, EMD-SSA, a hybrid data-adaptive multivariate multiscale method based on empirical mode decomposition (EMD) and singular spectrum analysis (SSA), is proposed to extract the non-linear trend present in the rainfall series. At the initial stage, EMD is applied to decompose the observed rainfall series into several intrinsic mode functions (IMFs) of different frequencies depicting trends and oscillatory patterns. Periodogram analysis of each IMF is performed by Lomb-Scargle spectral analysis to identify the important periodic signals and their period. These periods are considered suitable input (embedding dimension) to the SSA. The rainfall data is collected on a daily scale for the region of Mumbai, India, from NASA’s Prediction of Worldwide Energy Resource (POWER) archive from 1981–2020. The non-linear trend present in the rainfall is estimated by the EMD, SSA, and EMD-SSA methods. From the analysis, an increasing rainfall trend is observed in the Mumbai city, indicating more rainfall events in the future. Finally, the study suggests that a hybrid EMD-SSA is better than standalone EMD and SSA approach. In the future, the proposed EMD-SSA can also be applied to understand the variabilities in rainfall pattern with respect to the climate indices.

 

 

How to cite: Shejule, P. and Pekkat, Dr. S.: Non-linear Rainfall Trend Extraction Using Hybrid Empirical Mode Decomposition And Singular Spectrum Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5363, https://doi.org/10.5194/egusphere-egu23-5363, 2023.

A.141
|
EGU23-634
|
ECS
Achala Singh, Priyank Sharma, and Ramesh Teegavarapu

Understanding the space-time variations and dependency between hydroclimatic variables is vital for predicting future changes towards adaptive water resources management in a changing climate. Globally, it is observed that the mean and extreme hydroclimatic conditions are experiencing a significant shift under a changing climate, which affects the spatio-temporal distribution of floods and droughts. However, climate change studies seldom talk about the time invariance of the characteristics of a hydroclimatic time series. This research assesses the time invariance of the statistical properties of hydroclimatic variables (such as rainfall, temperature, streamflow and their derived indices) for a tropical river basin (i.e., the Tapi River basin) in India. Climate change profoundly impacts tropical river systems. Hence, assessing and detecting stationarity in hydrologic processes for such a river basin is imperative to predicting future changes. In this study, we have analyzed nine hydroclimatic variables representing the mean and extreme rainfall, temperature and streamflow. The hydroclimatic indices have been statistically examined to detect stationarity, homogeneity, and trends. A non-overlapping block stratified random sampling approach has been applied to identify the time invariance of hydroclimatic indices. The stationarity assessment approach investigates the similarities in the median, variance, distribution, and statistical moments of the continuous time series data. Based on the results of this study, weak and strict stationarity can be identified. The findings have significant ramifications for the planning and design of hydraulic structures, stormwater networks, flood mitigation, and disaster management for the Tapi basin.

How to cite: Singh, A., Sharma, P., and Teegavarapu, R.: Stationarity assessment of hydroclimatic variables for a tropical river basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-634, https://doi.org/10.5194/egusphere-egu23-634, 2023.

A.142
|
EGU23-9458
|
ECS
|
Highlight
|
Nicolò Montanari

The rainfall time series in Bologna is one of the longest daily precipitation records available.

Figure 1 presents the progress along time of cumulative annual rainfall during the observation period. Dating back to 1813 with no missing values, the time series spans over 208 years. As such, it offers a valuable opportunity to evaluate long term trends of rainfall statistics, thus offering information on past and recent precipitation changes.

In detail, we focus on the progress along time of annual and monthly precipitation as well as the annual and monthly maxima of daily precipitation, by applying linear regression. We also present an overview of historical long term droughts and estimate their frequency of occurrence by applying run theory. We also compare drought statistics of historical data with those of future climate scenarios recently presented by the literature.

The results highlight that the drought frequency is decreased in the past 50 years, while there is evidence of decreasing variability of annual rainfall during time, with no evident trend.

How to cite: Montanari, N.: Long term trends in the Bologna daily rainfall time series (1813-2020), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9458, https://doi.org/10.5194/egusphere-egu23-9458, 2023.

A.143
|
EGU23-13123
Ramesh Teegavarapu, Priyank Sharma, and Diego Li

Stationarity assessments of annual extremes of monthly precipitation and minimum, average, and maximum temperatures at over 1200 sites in the U.S. are carried out using a nonoverlapping block stratified random sampling approach. The approach uses random partitioning of the time series into several blocks to assess different forms (i.e., weak, strong) of stationarity using nonparametric two-sample and multi-sample hypothesis tests. This approach's assessment of stationarity is compared with those derived from nonparametric Spearman’s rank correlation and variants of Mann-Kendall tests considering seasonality and autocorrelation. Monthly data of precipitation and temperature obtained from the United States Historical Climatology Network (USHCN) for the period 1910-2019 are used for this analysis. Tests (e.g.,  Augmented Dickey-Fuller (ADF) and Kwiatkowski-Phillips-Schmidt-Shin (KPSS)) specifically geared for stationarity assessments in econometrics and time series forecasting are also used for comparative assessment. Discrepancies in assessments from the nonparametric tests, ADF and KPSS, and nonoverlapping random sampling approach are noted in the number of sites. The random sampling approach used in the current study provides a robust assessment of stationarity considering the different characteristics of the hydroclimatic time series.

How to cite: Teegavarapu, R., Sharma, P., and Li, D.: Stationarity Assessment of Precipitation and Temperature Extremes in the Continental United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13123, https://doi.org/10.5194/egusphere-egu23-13123, 2023.

A.144
|
EGU23-11599
|
ECS
|
Highlight
Luisa Schmidt, Wantong Li, and Matthias Forkel

Climate change leads to a change of precipitation frequency and quantity as well as to increased temperature inducing extreme weather events like floods but also more intensive and longer drought periods.

The response of the vegetation to these trends is of high interest because vegetation regulates interception, transpiration and is a water storage which is important for plant productivity, agriculture, carbon cycling and the danger of wild fire occurrence. Reduced precipitation in combination with increased temperature lead to water stressed vegetation which might not only behave different in regards of evapotranspiration but are also prone to wildfires. However, currently we don’t know how the water status changes in the long-term. A long-term time series of the vegetation leaf moisture content can help to understand the consequences of changing environmental conditions on the vegetation layer as part of the water as well as the carbon cycle.

Measurements of vegetation leaf moisture are usually only available for single test-sites (missing spatial coverage), often measured for a short time span and might hold missing data. Estimations of vegetation leaf moisture are able to provide consistent time series but are mostly done on regional scale which are also missing spatial transferability. However, long-term data with a consistent time series and large spatial coverage are necessary to address a reliable time series analyses in the context of climate change.

Our trend analysis will focus on the live-fuel moisture content (LFMC) which is based on the vegetation optical depth (VOD) and Leaf Area Index (LAI). LFMC is defined as the water mass of living vegetation to the dry mass of the vegetation, usually expressed in percentage. LFMC is an important variable in the field of wild fire analyses as it is one of the key predictors for risk and development of a fire. LFMC can be estimated on ecosystem level due to its independence of plant type. Here we use VODCA VOD and GLOBMAP LAI data to create a longer time series of LFMC for the period 1988-2017 on global scale to analyse temporal changes in LFMC. Initial results indicate a heterogeneous pattern of LFMC trends which depend on land cover type, e.g., with a decreasing trend for shrublands but an increasing trend for needle-leaved forests. We compare the trends in LFMC with trends in heat and drought events as well as fire weather indices. Inter-annual changes in LFMC correspond to multi-year drought events.

How to cite: Schmidt, L., Li, W., and Forkel, M.: Global trends of vegetation leaf moisture content and extreme weather since the 1980s, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11599, https://doi.org/10.5194/egusphere-egu23-11599, 2023.

A.145
|
EGU23-14073
|
ECS
Sunghun Kim, Heechul Kim, Ju-Young Shin, and Jun-Haeng Heo

This study attempts to estimate the extreme rainfall quantiles using the Intergovernmental Panel on Climate Change (IPCC)'s latest Coupled Model Intercomparison Project Phase 6 (CMIP6) and Coupled Model Intercomparison Project Phase 5 (CMIP5) models. In general, applied climate change research is carried out using numerical simulation data from various general climate models (GCMs). In this study, the precipitation data were obtained from CMIP5 and CMIP6 webpages of the World Climate Research Programme (WCRP). For the same GCM models, the Representative Concentration Pathways (RCP) scenarios (RCP4.5, RCP8.5) and Shared Socioeconomic Pathways (SSP) scenarios (SSP2-4.5, SSP5-8.5) were compared. The simple quantile mapping (SQM) method was applied for bias correction, and the at-site frequency analysis was performed for rainfall quantile estimation. In addition, the L-moments approach was applied to estimate the parameters, and the generalized extreme value (GEV) distribution was employed as the appropriate probability distribution. As a result, rainfall quantiles were estimated for each same GCM, and the change effects of different scenarios in the study area were quantitatively compared.

How to cite: Kim, S., Kim, H., Shin, J.-Y., and Heo, J.-H.: Comparison and Future Projection for Rainfall Quantile based on CMIP6 and CMIP5: Focusing on the Seomjingang River Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14073, https://doi.org/10.5194/egusphere-egu23-14073, 2023.

A.146
|
EGU23-15368
|
ECS
Jue Zeng, Xudong Fu, and Hongchang Hu

Historical streamflow reconstruction based on the pre-instrumental data for rivers in Tibet can provide long-term perspectives on the impact of the climate change in the Third Pole on Earth.  We use the VIC model to reconstruct the yearly, monthly and daily streamflow of Lhasa River during the past 5 centuries (1473~2017). Compared with the recent 60 years, the past 500 years have 11% more average annual runoff. Signals of long-term variations have been detected including a 60 years cycle and decades of continuous wet/dry years. The streamflow shows almost 50% higher annual and daily maximum runoff and highly variable in the 16th and 17th centuries, and decreased and more stable runoff thereafter till the present. These findings conform to the understanding of climate change in this area: the combined effects of Indian Summer monsoon and mid-latitude Westerlies, and confirms the potential of exploring the historical streamflow features using the VIC model and paleo-climate data. They also reveal the limitation of the recent instrumental records for understanding the long-term hydrological behavior of rivers in Tibet.

How to cite: Zeng, J., Fu, X., and Hu, H.: Streamflow reconstruction and its long-term variation characteristics in Lhasa River Basin over the past 5 centuries (1473~2017), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15368, https://doi.org/10.5194/egusphere-egu23-15368, 2023.

Posters virtual: Tue, 25 Apr, 10:45–12:30 | vHall HS

Chairpersons: Ramesh Teegavarapu, Priyank Sharma
vHS.29
|
EGU23-11681
|
ECS
|
Highlight
|
Daneti Arun Sourya and Meenu Ramadas

Estimation of reference evapotranspiration (ETo) is necessary for hydrological modeling, water stress adaptation and agricultural water management. While numerous studies have addressed changes in temperature and precipitation patterns at different spatiotemporal scales for assessing hydroclimatic variability, similar analyses on regional evapotranspiration trends are limited. This can be attributed to lack of observed records of ETo at regional scales, and highlights the need for developing better models for estimating this variable. To address this research gap, we developed monthly 0.5° gridded ETo dataset for entire Germany using machine learning techniques and then investigated the temporal trends in ETo over the region. We utilized flux tower data (sensible heat flux, net radiation, soil heat flux, and latent heat flux) from multiple locations in the region to compute observed ETo using the surface energy balance method. Then, fed-forward back-propagation method (BPNN) is used for predicting monthly ETo with easily available input predictors such maximum temperature, minimum temperature, precipitation, soil moisture, short wave radiation, and wind speed. The BPNN is trained with various input combinations in order to estimate ETo with minimal input predictors, and their performance is assessed using metrics: coefficient of determination, mean absolute error, and root mean square error. The results showed that with all the input parameters, the coefficient of determination  for training and testing are 0.89 and 0.93 respectively, while the best parsimonious model (precipitation and downward shortwave radiation as predictors) gives 0.88 and 0.93 respectively. Gridded ETo estimated using the best parsimonious model is then used for assessing spatially varying trends in the variable at monthly and annual time scales over Germany using Mann-Kendall test and Sen’s slope. The long term analysis helps us to identify critical regions in the study area that needs attention for water resources management, drought mitigation and improved adaptation to changing climate.

Keywords: Reference Evapotranspiration, Flux Tower, Surface Energy Balance, Feed Forward Back Propagation (BPNN), Trend Analysis, Mann-Kendall Test

How to cite: Sourya, D. A. and Ramadas, M.: Development of gridded monthly reference evapotranspiration dataset for Germany for long term trend analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11681, https://doi.org/10.5194/egusphere-egu23-11681, 2023.