Bangladesh, India and Nepal - which all experienced major flooding in 2017 - could all be among the nations experiencing the greatest need, the charity warned.
It also flagged the displacement of Rohingya refugees, and the continuing civil war in Yemen as further major causes of concern, heading into 2018.
Explaining the scale of the need already existing in some areas, CEO Nigel Harris told Premier: "So of this is absolute visceral need.
"We need to feed people, we need to sustain life, we need to help those emergency situations by providing water [and] sanitation."
2018 could be the worst year ever in terms of humanitarian need, according to the United Nations, which says 135 million people are currently in desperate need.
Tearfund also fears countries in the Sahel region of Africa - Burkina Faso, Chad, Mali and Niger - could require further assistance following low rainfall levels in 2017, while similar issues are affecting parts of Somalia.
It said the Central African Republic and the Democratic Republic of Congo remain "incredibly vulnerable" due to political unrest and worsening violence, while Boko Haram remain a major source of concern in Nigeria.
The charity raised concern about unrest and fighting in South Sudan and Burundi, and it highlighted the need for support for families starting to return to Iraq.
Mr Harris added: "Please pray for governments in Central African Republic, South Sudan, DRC, Yemen and Iraq to reach peaceful solutions and, of course, for all of us, to react to this ongoing situation of climate change."
Click here to listen to Premier's Marcus Jones speaking with Tearfund's Nigel Harris: