Blue and green water: why they affect us all

Address­ing the water crisis is imper­at­ive for glob­al cli­mate adapt­a­tion. Cur­rent water policies focus primar­ily on vis­ible, or « blue, » water sources, often over­look­ing the crit­ic­al role of « green » water, stored in soil and veget­a­tion, con­sti­tut­ing about 60% of glob­al land pre­cip­it­a­tion. Recog­nising water as a Glob­al Com­mon Good (GCG) is essen­tial for achiev­ing cli­mate goals and Sus­tain­able Devel­op­ment Goals (SDGs).

At COP29, nego­ti­ations aim to achieve agree­ments to respond to the water crisis adequately; how­ever, to do so, a prop­er under­stand­ing of the under­ly­ing hydro­lo­gic­al cycle is neces­sary. The water, or hydro­lo­gic­al cycle, is under­stood as “[…] a com­plex sys­tem with dif­fer­ent stores inter­act­ing with vary­ing strengths and over a wide range of scales with oth­er com­pon­ents of the Earth sys­tem such as atmo­sphere, bio­sphere, and litho­sphere¹”  and it is driv­en by sol­ar radi­ation and grav­ity, with water chan­ging into dif­fer­ent states (liquid, gas, sol­id) and mov­ing between the atmo­sphere, ocean and land. It evap­or­ates and tran­spires from land and water bod­ies, then gets trans­por­ted, con­densed, and ulti­mately pre­cip­it­ates back onto the Earth’s surface.

World­wide, we are cur­rently push­ing the hydro­lo­gic­al cycle out of bal­ance. Through human-induced cli­mate change, defor­est­a­tion, and loss of biod­iversity, we are chan­ging pre­cip­it­a­tion pat­terns. As tem­per­at­ure rises, the cycle intens­i­fies and evap­or­ates more water lead­ing to more extreme weath­er events, like extreme rain­fall, hur­ricanes and coastal floods². 

Cur­rent water policies primar­ily focus on vis­ible water sources, such as rivers and oceans (blue water), while fre­quently neg­lect­ing the import­ance of green water. Non­ethe­less, sci­entif­ic evid­ence shows that around 60% of the pre­cip­it­a­tion that falls on land ends up stored as green water ‑fur­ther indic­at­ing that green water is the largest con­trib­ut­or to fresh­wa­ter glob­ally³. The import­ance of green water is fur­ther addressed by Fried­ling­stein et al⁴., who high­light that green water in soils is of neces­sity for land-based eco­sys­tems, which can absorb 25–30% of car­bon diox­ide emit­ted from fossil fuels.

Fig­ure 1 rep­res­ents the glob­al net­work of ter­restri­al mois­ture flows between dif­fer­ent regions, show­ing how inter­con­nec­ted our world is via wind rivers. The arrows rep­res­ent the dir­ec­tion of mois­ture flow, through two pro­cesses: evapo­tran­spir­a­tion, the pro­cess where water is trans­ferred from land to the atmo­sphere by evap­or­a­tion and tran­spir­a­tion (from plants), and pre­cip­it­a­tion, mois­ture that returns to the land as rain­fall. There are also points present­ing the geo­graph­ic­al centre of each coun­try to demon­strate that water evapo­tran­spires and pre­cip­it­ates from every coun­try towards the rest of the world. Hence, the net­work show­cases that coun­tries are highly inter­con­nec­ted when it comes to mois­ture flows. This is sci­entif­ic evid­ence that water evap­or­ated from one region with­in a coun­try can sig­ni­fic­antly impact rain­fall in dis­tant regions; coun­tries are even more inter­con­nec­ted in terms of the hydro­lo­gic­al cycle than pre­vi­ously thought.

Sim­il­ar to river basins and aquifers, atmo­spher­ic mois­ture car­ries water from one coun­try to anoth­er, across oceans and con­tin­ents⁵, mean­ing that wind rivers can be tracked to demon­strate how eco­nom­ic activ­it­ies tak­ing place in one region or coun­try can impact oth­ers down­wind.

For example, water evap­or­a­tion in West Africa is trans­por­ted down­wind to the Amazon Rain­forest (mostly Brazil), where it arrives in the form of rain­fall. Now, in the last dec­ade, Brazil has pro­moted policies of heavy deple­tion of the Amazon Rainforest’s resources, which are lead­ing to a loss of green water avail­ab­il­ity as the land’s capa­city to store and use green water dis­ap­pears. Hence, there is less green water that can be evap­or­ated in the Amazon Rain­forest to be trans­por­ted fur­ther down­wind to neigh­bour­ing coun­tries. This is the case in coun­tries such as Colom­bia, which rely heav­ily on rain­fall water for con­sump­tion and energy pro­duc­tion since resource deple­tion in Brazil has led to a lower water yield⁶. 

Glob­al inter­con­nec­tion in the water cycle is a fact, and it means we must start address­ing the water crisis hol­ist­ic­ally where both green and blue water are at the fore­front of glob­al-scale policies and pacts.

If water is part of this com­plex sys­tem called the hydro­lo­gic­al ‑or water- cycle, gov­ern­ing it requires a shift in per­cep­tion of the way it is con­ceived. Water must be increas­ingly under­stood as a Glob­al Com­mon Good (GCG). But what exactly does this concept entail?

First, recog­nising water as a GCC is acknow­ledging that com­munit­ies, coun­tries, and regions are inter­con­nec­ted, not only through vis­ible water resources (blue water, such as rivers and lakes) but also through atmo­spher­ic mois­ture flows and green water (water stored in soil and veget­a­tion). Second, this shift pos­i­tions water high up in the inter­na­tion­al agenda since it under­stands that the Anthropocene’s impact on the hydro­lo­gic­al cycle is intric­ately con­nec­ted with the pres­sure it puts on oth­er alarm­ing pro­cesses such as cli­mate change and biod­iversity loss; for instance, a stable sup­ply of green water is cru­cial for absorb­ing car­bon diox­ide and sup­port­ing ecosystems.

Moreover, this concept avoids treat­ing water in a siloed man­ner when it comes to SDGs. The water crisis is not only an issue to solve via SDG 6 – which mostly deals with WASH (Water, san­it­a­tion and hygiene). Water is fun­da­ment­al to achiev­ing vir­tu­ally all the SDGs since a destabil­ised hydro­lo­gic­al cycle threatens food secur­ity, eco­nom­ic sta­bil­ity, pub­lic health, and social equity, which are corner­stones of sus­tain­able devel­op­ment⁷.

At COP29 in Baku, nego­ti­at­ors had a unique oppor­tun­ity to pro­mote an integ­rated approach to solve the water crisis and lay found­a­tion­al steps towards a uni­fied Glob­al Water Pact by agree­ing to the Baku Declar­a­tion on Water.

Dur­ing Novem­ber 19^th (the day ded­ic­ated to food, agri­cul­ture, and water) key inputs were dis­cussed for the Declar­a­tion. A cru­cial first out­come was the com­mit­ment to “[…] pro­mote dia­logue and part­ner­ships [by] strength­en­ing COP-to-COP syn­er­gies [and] sup­port­ing the devel­op­ment of col­lab­or­at­ive and aligned cli­mate action policy⁸”. This com­mit­ment is a mile­stone in estab­lish­ing a Glob­al Water Pact as it places the hydro­lo­gic­al cycle as a whole at the heart of the Rio Trio – UNFCCC, UNCBD and UNCCD. After all, we know water secur­ity, con­ser­va­tion, and sus­tain­able man­age­ment must be treated integ­rally to achieve cli­mate goals⁹.

The Declar­a­tion on Water, also framed water as a found­a­tion­al ele­ment in cli­mate action, as it asks coun­tries to com­mit to “[…] effect­ively integ­rate water con­sid­er­a­tions in the design of cli­mate policies, includ­ing nation­al adapt­a­tion plans (NAPs) or strategies, nation­ally determ­ined con­tri­bu­tions (NDCs), and asso­ci­ated imple­ment­a­tion plans, as well as nation­al biod­iversity strategies and action plans (NBSAPs) […]”. Now, the declar­a­tion was not expli­cit on the need to set clear glob­al tar­gets related to water con­ser­va­tion in its green and blue forms, lim­it­ing the sup­port for inter­na­tion­al pro­gress quan­ti­fic­a­tion policies, a cru­cial aspect for a well-designed Glob­al Water Pact¹⁰.

Fin­an­cial com­mit­ments were lack­ing on the Declar­a­tion on Water. For a Glob­al Water Pact to become a real­ity, both, coun­tries and fin­an­cial insti­tu­tions need to pledge invest­ments in sus­tain­able water infra­struc­ture, innov­at­ive tech­no­lo­gies, and con­ser­va­tion efforts, which the Declar­a­tion does not back. Addi­tion­ally, the need for trans­par­ency and account­ab­il­ity around water and its resource-related uses (such as defor­est­a­tion and energy pro­duc­tion) was not expli­citly stated. Hence, back­ing pro­pos­als such as the stand­ard­isa­tion of data shar­ing pro­cess, green and blue water foot­print dis­clos­ures, and sus­tain­able cor­por­ate water prac­tices, which facil­it­ate busi­nesses’ account­ab­il­ity in terms of impact to the hydro­lo­gic­al cycle¹¹ becomes harder.

A big win in terms of social inclu­sion was achieved on the Declar­a­tion on Water. The fifty sig­nat­ory coun­tries agreed to include the need to incor­por­ate per­spect­ives from often mar­gin­al­ised com­munit­ies such as indi­gen­ous peoples, migrants and youth. A Glob­al Water Pact will inher­ently need these voices to shape suc­cess­ful policies that pro­tect loc­al water resources in their blue and green forms and respect tra­di­tion­al know­ledge since indi­gen­ous com­munit­ies are stew­ards of nat­ur­al resources, and young people are heirs of the con­sequences of today’s water policies¹².

As sci­entif­ic evid­ence proves that the hydro­lo­gic­al cycle con­nects coun­tries and regions far more deeply than pre­vi­ously thought, a Glob­al Water Pact seems to be the most ambi­tious, yet cru­cial way to address the water crisis. COP29 had a key oppor­tun­ity: to ini­ti­ate a form­al roadmap toward a Glob­al Water Pact by out­lining the role of water in cli­mate action.

By no means is this declar­a­tion per­fect: it does not pro­mote a frame­work for water and cli­mate fin­ance, and it misses the chance of back­ing set goals for cli­mate action. Yet, the Declar­a­tion also sup­ports the need for COP-to-COP col­lab­or­a­tion, pro­motes the integ­ra­tion of water – impli­citly both blue and green – on nation­al devel­op­ment plans, and calls for the voice of indi­gen­ous peoples and youth to be at the fore­front of the debate. Over­all, the Declar­a­tion on Water for Cli­mate action signed at Baku dur­ing COP29 increases the momentum that water has gained in the past few years at the inter­na­tion­al scale and as UNCCD (the key COP for water action) approaches, the inter­na­tion­al com­munity should fol­low closely the steps those coun­tries will take to keep increas­ing water vis­ib­il­ity on the inter­na­tion­al agenda.