ReaLSAT, a global dataset of reservoir and lake surface area variations

Lakes and reservoirs, as most humans experience and use them, are dynamic bodies of water, with surface extents that increase and decrease with seasonal precipitation patterns, long-term changes in climate, and human management decisions. This paper presents a new global dataset that contains the location and surface area variations of 683,734 medium-sized (0.1 - 100 sq. km.) lakes and reservoirs (south of 50°N) from 1984 to 2015, to enable the study of the impact of human actions and climate change on freshwater availability. Within its scope for size and region covered, this dataset is far more comprehensive than existing datasets such as HydroLakes. While HydroLAKES only provides a static shape, the proposed dataset also has a timeseries of surface area and a shapefile containing monthly shapes for each lake. The paper presents the development and evaluation of this dataset and highlights the utility of novel machine learning techniques in addressing the inherent challenges in transforming satellite imagery to dynamic global surface water maps.

Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past two decades, primarily as a result of the phaseout of ozone depleting substances under the Montreal Protocol and the use of HFCs as their replacements. Projections from 2015 showed large increases in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 °C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2-eq inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2-eq yr−1) but are about 20 % lower than previously projected for 2017–2019, mainly because of lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and lower reported consumption of HFC-143a in China. Because this time-period preceded the beginning of the Kigali controls, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications, in anticipation of national or global mandates. A new HFC scenario is developed based on current trends in HFC use and current policies in several countries. These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2-eq yr−1 to 1.9–3.6 GtCO2-eq yr−1. The provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2-eq yr−1 in 2050. Without current policies, HFCs would be projected to contribute 0.28–0.44 °C to the global surface warming in 2100, compared to 0.14–0.31 °C with current policies, but without the Kigali Amendment. In contrast, the Kigali Amendment controls are expected to limit surface warming from HFCs to about 0.04 °C in 2100.

Modelling Dynamic Hydrological Connectivity in the Zoigê Area (China) Based on Multi-Temporal Surface Water Observation

The sustainability of wetlands is threatened by the past and present land use practices. Hydrological connectivity is one of the most important aspects to consider for wetland rehabilitation planning purposes. Circuit theory and connectivity indices can be used to model and assess hydrological connectivity. The aim of this study was to assess spatiotemporal variation in the hydrological connectivity of the Zoigê area from 2000–2019 using both methods. The study area contains a Ramsar wetland of international importance, namely the Sichuan Ruoergai Wetland National Nature Reserve. We used a global surface water observation product as the major input for both methods, and then analyzed the temporal and spatial characteristics, in terms of important components and patches. We found that the overall connectivity has increased slightly in the last 20 years, while the probability of connection between patches of surface water has increased significantly. Important components and patches represent steppingstone habitat for the dispersal of organisms in the landscape. The main determinants of hydrological connectivity are mostly human oriented, predominantly a decrease in large livestock population size and population increase.

Identifikasi Genangan Banjir di Wilayah DKI Jakarta Menggunakan Citra Satelit Sentinel-1

Provinsi DKI Jakarta merupakan wilayah dengan karakteristik topografi yang berada pada kemiringan lereng relatif landai dan terletak pada dataran rendah. Hal ini menyebabkan wilayah Jakarta menjadi semakin rentan tergenang air dan banjir pada musim hujan. Pada awal tahun 2020, Jakarta mengalami banjir yang diakibatkan oleh hujan lebat yang turun sejak 31 Desember 2019 hingga 1 Januari 2020. Untuk keperluan antisipasi dan mitigasi bencana terkait banjir tersebut diperlukan ketersediaan data tentang luas genangan banjir dan letaknya secara cepat. Salah satu teknologi yang potensial untuk diterapkan adalah menggunakan citra satelit Sentinel-1. Berdasarkan kondisi tersebut, telah dilakukan kajian untuk mendeteksi daerah terdampak genangan banjir dari citra satelit Sentinel-1. Adapun teknik yang digunakan adalah metode change detection dan thresholding. Pada kajian ini digunakan citra Sentinel-1 perekaman tahun 2019 dan 2020, DEMNAS, Global Surface Water dan batas administrasi wilayah DKI Jakarta. Adapun tahapan pelaksanaan kajian mencakup proses change detection dengan ratio image dari dua citra Sentinel-1 GRD sebelum dan saat banjir, perhitungan nilai optimum threshold untuk menentukan banjir dan tidak banjir, masking banjir, dan perhitungan luas genangan. Berdasarkan hasil kajian diperoleh luas total daerah yang terkena banjir sekitar 1.156,84 hektar, sedangkan luas area banjir dari data Pemprov DKI sekitar 12.896,35 hektar. Hasil validasi menggunakan data Pemprov DKI dengan membandingan antara citra Sentinel-1 tahun 2019 dan 2020, diperoleh hasil 61 lokasi atau sekitar 28,96% termasuk ke dalam hasil interpretasi kelas banjir dan terdapat 157 lokasi atau sekitar 71,04% termasuk ke dalam hasil interpretasi kelas tidak banjir.

The Surface Longwave Cloud Radiative Effect derived from Space Lidar Observations

Clouds warm the surface in the longwave (LW) and this warming effect can be quantified through the surface LW cloud radiative effect (CRE). The global surface LW CRE is estimated using long-term observations from space-based radiometers (2000–2021) but has some bias over continents and icy surfaces. It is also estimated globally using the combination of radar, lidar and space-based radiometer over the 5–year period ending in 2011. To develop a more reliable long time series of surface LW CRE over continental and icy surfaces, we propose new estimates of the global surface LW CRE from space-based lidar observations. We show from 1D atmospheric column radiative transfer calculations, that surface LW CRE linearly decreases with increasing cloud altitude. These computations allow us to establish simple relationships between surface LW CRE, and five cloud properties that are well observed by the CALIPSO space-based lidar: opaque cloud cover and altitude, and thin cloud cover, altitude, and emissivity. We use these relationships to retrieve the surface LW CRE at global scale over the 2008–2020 time period (27 Wm−2). We evaluate this new surface LW CRE product by comparing it to existing satellite-derived products globally on instantaneous collocated data at footprint scale and on global averages, as well as to ground-based observations at specific locations. Our estimate appears to be an improvement over others as it appropriately capture the surface LW CRE annual variability over bright polar surfaces and it provides a dataset of more than 13 years long.

Changes in solar activity based on radiocarbon data and climate variations in the interval 8000 - 1000 BC

This work examines the change in the activity of the Sun based on the reconstruction of the heliospheric modulation potential in the time interval 8000 - 1000 BC. Reconstructions of this potential were obtained using radiocarbon data, taking into account the influence of changes in the Earth’s climate. A comparison is made of the variations in the activity of the Sun with the global surface temperature. It is shown that variations in global temperature during this period could be the result of changes in solar activity. So high solar activity could lead to recorded temperature maximums around 7000 and 5300 BC. The drop in temperature in the range 3000-1000BC could be the result of low solar activity.